I've bought lots of devices over the years. VV, VW and Mech mods.
Most I've given away because they weren't for me.
Some I've sold at a loss.
Some I've just thrown away because they were complete junk or not safe for anyone to use.
There's only one mod I've bought multiples of and thats the Full size ProVari. To be fair though, I tend to buy them from the Classified section and try to only spend $85 or so on them. I like to take them apart, strip the paint off with scotchbrite leaving the paint only in the milled sections of the tube and reassemble them. One I completly stripped and then polished up and made super shiny.
I still have five or six other devices, but the ProVari is my device in use 90% of the time.
I've got a copuple of bottom fed mods (a Reo Grand LP a Peko and a Geyscano), an egrip (ugh, why did I even buy this), and an IPV Mini. They all do what they are designed to do, some better than others. Some of these are poorly designed (egrip), some are poorly manufactured (Geyscano), some have cosmetic/paint issues(IPV MIni), but they all work.
I will probably continue buying devices that look interesting to try, but I resign myself going in that I'm probably going to be disappointed in some respect if I compare them to a ProVari, but that's OK because they are generally cheap enough that I don't really get to hung up about it.
Use whatever you like and works for you. Not everybody sub-ohms all the time. It's not an issue or selling point for everyone.