I currently mostly use Kayfun Mini V3 clones, including a KF Mini V3 Plus which I have just recently started playing around with - mainly for the somewhat larger juice capacity. The KF Mini V3s are all pretty good MTL RTAs.
I've also tried the Mini Goblin V3, Mini Serpent, and Augvapes Merlin with their airflow restriction devices in place for MTL draw. The velocity decks on those were all very nice to build on, but all of those RTAs had problems leaking. The KF Mini V3s (despite all being clones) have been much more dependable. I'm still looking into trying some newer MTL RTAs, like the 22mm Digiflavor Siren GTA.
Before that I used Kabuki clones and Nautilus Mini clearomizer tanks for quite awhile, just with various factory built BVC heads that have been available for them - including their TC heads, which sucked eggs. I figured TC MTL vaping was pie-in-the-sky BS because of that, unless I wanted to rebuild - which I did not. I never tried the aftermarket Nautilus/Kabuki RTA deck, though I was aware of them.
I hadn't used an RTA since several years ago when I got and used a Kayfun Mini Lite Plus for awhile. It vaped well (very well, for the time), but rewicking and refilling was a pain. It seriously "burned through juice" compared to what I was used to, so I had to refill it frequently through a small screw hole in the bottom of the device. I am frequently out and about, often driving for hours, so using an RTA like that regularly just wasn't practical.
So I stopped rebuilding and started using the Nautilus Minis and Kabuki clones, which was still a big improvement over the iClear 16 clearomizers I had been using before that. And before that...it's been so long I can barely remember - I used some kind of eGo type dual coil (oh, wow!) clearomizer. Before that it was m401 series cigalikes, using pre-cartomizer cartridges and separate atomizers. Those had a juice capacity of like 0.5ml, and the batteries were maybe 125-150mah? (It's been awhile. I can't remember exactly. Maybe they were 175mah?)
Even back then people were saying I needed to step up to eGo sized batteries, which I eventually did. Having to press a button to vape though, man, that took awhile to get used to, or so I thought it would, but it really only took about a day. Silly me. It took maybe two years since I started vaping 7 or so years ago to make that simple transition.
I, and the rest of us, have come a long way since then. I've only recently (within the last 6 months or so) got back into rebuilding - specifically to do TC MTL builds. Those above mentioned RTAs are what I started out with in that effort. My first TC mod was an IPV D2 for using Nautilus TC factory coil heads in my Kabuki clones. At the time, I found that box mod to be a bit big and heavy - compared to an Innokin iTase vv3 or iStick Mini, which are what I was using before. (Yes, to power those "large" Nautilus Minis and Kabuki clones, as well as the more size appropriate little iClear 16s.)
Then I got some Brazilian Zebra wood TC box mod that was super lightweight (I forget the name of it), but the SS buttons rattled maddeningly on that device, so I gave that away to my oldest daughter - who was just getting into vaping to quit using a hookah. After that I got my first iStick Pico 75W, then I like that so much I got a 2nd one. That's what I currently use.
But I was still mostly doing wattage power mode builds with Kanthal. TC MTL builds took me awhile to get comfortable with using SS wire. One of my main hang ups was getting used to the fact that I did not need above ohm builds to do good TC MTL. Now I do below ohm SS TC builds all the time, but I know I could be doing better with more appropriate wire, and using a higher end mod - though I know that last is not absolutely necessary.
A typical SS TC MTL build for me now has a 2.5 to 3mm ID coil, so I have sufficient wick capacity for chain vaping high VG tobacco flavor juices. I don't do NET flavored juices. I do about 7-9 wraps, depending on the wire gauge I use, which is typically 26 or 28 gauge. 30 gauge tends to deform/bend a bit too much, a bit too easily, but is okay. I typically don't use it anymore. 24 gauge seems unnecessarily thick for my needs, but that could change using a different wire material. My SS TC builds range from about 0.5 to 0.9 ohms.
Higher resistance TC builds tend to be more accurate, but not always that much more accurate as to matter much - depending on what wire you are using (its TCR) and other factors. Too high a resistance build and you get up to where your TC board won't want to play nice, and so you get kicked back into regular wattage mode. Luckily, when using SS wire that is not a big issue - which is probably why I've stuck with using it exclusively for awhile now. But SS still kind of sucks, as a cheap board won't read its small resistance variations very well (or often enough, or whatever) leading to inconsistent power delivery.
Thinner gauge wire can also help with TC accuracy, so it is typically best to use the thinnest wire that still suits all your other build needs. Twisted, Clapton and other such fancy wire are a whole other ball game. I've tried using double twisted SS wire, but the deck screws on a KF Mini V3 don't clamp down on the wire very well - leading to all sorts of problematic connection issues that were too big a pain to deal with. I've heard twisted SS wire can work well for TC, but the KF Mini V3's deck screws are too tiny to accommodate such wire nicely.
I switch between using rayon and cotton wick. Wicking with rayon can be a pain, but when done right it does wick better than any cotton out there. It's just hard to wick right, so sometimes I fall back on using something like Cotton Bacon v2. Cotton like that works pretty well, but burns more easily than rayon - which limits my vape more, so then I bounce back to trying rayon again. But if not done right, rayon sucks compared to cotton, and so on and so forth.
That's about where I am these days with TC MTL. Despite how it sounds, I'm actually doing fine with it, but I am always looking to do even better.
Update Edit: Sorry, I forgot to mention my power needs. Though I can, sometimes, MTL chain vape as much as 30ml a day in juice, I am okay using a single 18650 or 26650 battery powered device. That is, as long as it is not a built-in battery type of mod, so I can easily change out the battery whenever necessary. On heavy vape days I end up switching out batteries every several hours. That doesn't bother me. I'd much rather do that than use a ginormous two or three battery mod.
I carry two extra charged batteries on me whenever I'm away from home, in silicone battery sleeves. I will carry 3 or more for overnight trips (though two extra is usually sufficient). Carrying around 2-3 extra 18650 batteries in my pocket does not bother me. I'm not sure how I will feel about carrying around two extra 26650 batteries on me all the time. Those things are pretty fat compared to an 18650.
I hardly ever charge via the USB port. Instead, I just switch out batteries as needed. I have a 4-battery charger at home. I have a single battery charger in my car at all times. And also a double battery charger to pack with me when going on extended trips - and as a backup for the other two chargers.
I've never used a dual or triple 18650 battery mod, and I would not want to. Typically I have one favorite mod, and that is the mod I use all the time - in or out of the house, regardless of what I am doing. That's just my preference, as it keeps my vaping life simple. So I like that device to be relatively small and light. I pack an extra one (not necessarily the same mod) as a backup for extended trips - like for when I went to Poland with my family for 3 weeks last year. (I took a bunch of vape gear with me on that trip, but didn't really need to take quite so much.)
