Halocigs G6, SmokelessImage Volt, Bloogplanet maxxfusion are all the same thing - I think they are all rubberized, manuals have a small partially recessed button, manual threaded end looks totally sealed, 40mah extra charge for each size vs those below, but a short 5 second cutoff (max length of drag or button press). 3.6v
Vapor4Life is the original style but with a custom 10-13 second cutoff, at least on the current single logo batteries (gold button) as noted in their description. if you think you will want long drags, buy these. 3.7v
Then there is the original black or white or steel manufacturer model, 5 second cutoff, 3.7v
All of these can use each others cartos.
Ego is something totally different - 510 threaded, less voltage than the above (3.4v), more charge, almost no prefilled cartomizers available vs the KR808D-1 models above which have lots of prefilled cartos.
My recommendation instead of Ego is the Riva 510 kits at Liberty-Flights.com because the kits there are all 3.7v. I put an adapter on (510 to 808) and vape KR808D-1 cartos on them too. And I use blank 510 cartos, and atomizer + drip tip to test juices. Not all Rivas are 3.7v - only the latest stock from one manufacturer is. At Liberty-Flights press the 20% off upper left front page and then shop at the lowered prices.
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Just decide which you want first
(because almost all vapers end up with more than one model)