I have a vivi on my LT now, the original 2.4ohm head has been going for 16 days now (@4.2-4.5v). Cinnamon, unknown, someone else will know that but they are a plastic so I'd be wary of "known to cause issues" juices. You can also get metal tanks, though they obviously don't have a window to see juice levels, and I've read that they can have leaking issues.
I only have the single one so far, another is arriving today. Why two? Why not! I like to have backups and am preferring the vivi over cartos, so would rather have another tank to fall back on if the first ever has major failure. Have two cartotanks on standby also, though they aren't my go-to.
I'd test out the heads (2.8mL came with 3 heads, 1.8-2.8ohm) and find out which you like, then buy replacements according to your preference. You can also recoil/wick them yourself. The resistance wire runs through a plastic cap, and can melt it. I'm fairly certain mine has done this, though it only tasted nasty for a few puffs and it's been fine since. Rebuilding with nr wire through the cap solves this issue I believe. I just found a local supply of nr wire (after spending saturday hitting up jewellery supply shops), but it's out of my way so will have to pick it up next saturday. Till then I'll settle with the included ones (probably still be on the original).
What I can tell you about them? So far they're my favourite method of
vaping my ADV. There are some issues and they aren't perfect. To start, the centre post was a little (~1/2mm) protruded on mine, which was pushing the centre pin on my LT down. I was finding myself needing to tighten it semi-regularly, eventually daily. After having to pull the centre pin on the LT up twice in a day I gently sanded the centre post down so it was flush with threads, rather break a feed than the body/tube. Had no issues since.
They can mute flavours, I haven't personally noticed this, but I'm mixing my own and I make them strong. The premix I used originally was 100VG and already quite mild, so I didn't notice any major difference with it either.
They need regular cleaning, I try to do it once every other day, if not once a day. They tend to make juice darker and somewhat thicker as you use them every few refills. Not as bad as my Vision V3s were, those turned juice into syrup half way through first fill. Darker juice may cause this sooner, but I don't have anything particularly dark to test. I noticed my premix 100VG juices would do this within 2 refills, but my DIY 60/40 (PG/VG) are lasting through 4 fills and the change is quite minor. Without knowing exactly what is in the premixes beyond 100VG I can't say what in them would cause this. I'm mainly cleaning it out of habit and as a pre emptive measure.
Luckily disassembling, cleaning, and reassembly takes around 5 minutes after you've done it once and know what's what. Some folks dry burn them after but I just shake everything, blow through post, dry everything with a paper towel (dab at wicks till towel comes off dry) and deal with "meh" vapes for the first couple minutes. It returns to normal operation pretty quickly.
Hm...well, there ya go, answered some questions you asked and some you had not. Hope it helps even if a little.