I own (and use) lots of bottom-feeders. In fact, I have 12 of them:
2 REOs---a 14500 original Mini and an 18490 Mini v2.1, sealed feed system
2 Phidias 18650 Woodies---upgraded from gravity-needle-feed to the newer no-needle sealed gravity feed system
2 MaximumVapors Luicy Juicies---3AA plastic box mods, dual-14500, regulated 5V
4 Vapage VMODs---two 18650 XLs and two 14500 2.0s---sealed gravity-feed systems
1 Old Goat---2AA plastic box mod, single 14500---needle-feed hose-in-bottle
1 Missy Wetbox---2AA plastic box mod, single 14500---needle-feed hose-in-bottle
Except for the two Luicy Juicy 5V regulated feeders, all the rest are 3.7 volt. I don't personally feel a need for variable voltage on my bottom-feeders, although I acknowledge that otherd may love bottom-feed VV. Heck, if I want VW, I've got a bunch of Kicks I could use.
I currently run both Phids, the REO Mini 2.1, the Old Goat, and the Wetbox with modified YK1 Mini RDAs from fasttech, which are $6 clones of the more expensive Cyclone Mini RDA. I converted the RDAs from dripping to bottom-fed by using a dremel and a #65 micro-bit to drill two juice-feed channels through the silicon insulator that surrounds the positive pin of the 510 connector. This modification doesn't cause shorting and works beautifully. These are all micro-coiled from 1.2 to 1.4 ohms.
The two Juicy Luicys run J1 Mini RDAs, also $6 from fasttech, modified for bottom-feeding the same way as the YK1 Minis, micro-coiled to 1.5 ohms.
The four VMODs are currently outfitted with Vapage Hybrid Slant-Coil atomizers, either 1.5 or 2.0 ohms, simply because those atties are perfectly matched to the sealed chamber side-feed system that Vapage uses. They will work with the YK1 Minis, however. Grind off about 1/8th inch of the barrel length of a shortie 510-to-510 open (unsealed) adapter, screw that onto the YK1 connector, then remove from the VMOD both the adapter cylinder and the screw-on cone that secures the aluminum body onto the plastic inner frame. The YK1 with the reduced-length open adapter is just the right length to secure the outer body and provide a good seal for the feed chamber.
OK, enough tech talk.
All my bottom feeders provide roughly the same vape, which varies mainly based on the atomizer and juice used. They differ in design, build quality, aesthetics, ergonomics, vape time between battery swaps, and price. The REOs and VMODs are all-mechanical, using no electrical switches or wiring, which doesn't make them infallible but is a plus in my book.
The Old Goat and Wetbox, now almost three years old, are cheap little plastic boxes essentially home-built by one modder. The Phids use beautiful woods and feel great in the hand. The VMODs are nicely designed but not as heavy-duty in build quality as they could be, while the REOs are, of course, the 800 lb. gorillas of bottom-feeders, milled from a solid block of aluminum and built to be indestructible.
The Old Goat was the least expensive---$20---but I've had to repair it often, replacing the both on-off and firing switches, and re-soldering the positive wire to the 510 connector on more than one occasion. The Old Goat also leaks like a sieve, since it uses an unsealed open needle-feed system. Same with the Phids. Their wiring needed re-soldering numerous times, and their gravity-needle-feed system leaked, but they've now been upgraded to a sealed tube-fed gravity system, so no more leaks with those. Curiously, the little Wetbox is also needle-fed but has never leaked or needed repair.
I love the loyalty of the army of REOnauts, but I ignore completely the small percentage of REO fanatics who imply loudly and often that you're an idiot if you own any bottom-feeder except a REO. Look, REOs are great. I love mine. Yes, they're expensive, but purchased used from the classifieds or new as blems (both of which I did), the cost is reasonable and justified, in my opinion. That said, I love all my bottom-feeders---the Old Goat for its blue LED, the Wetbox because it's like the Energizer Bunny and just keeps going and going and going, the Phids for their beauty, the Juicy Luicies for their extra power, and the REOs for their astonishing build quality.
In addition, there are many other bottom-feeders I don't own: Red Sky mods, Bogger Boxes, SweetVape mods, Grip mods, Monkey Boxxes, DNA-20 feeder mods, various other high-end custom American and European boxes, and even specialty tanks that screw right onto tube APVs to convert them to bottom-feeders.
Vaping has become a huge consumer marketplace, and bottom-feeders hold a meaningful niche in that market. Anyone who wants a bottom-feeder should definitely consider getting one.