I was pretty happy with ProTanks, but out of curiosity, like you seeing lots of recommendations, got an IBTanked to try out.
I found
a) INITIALLY seemed like MORE trouble to fill - just a little bit more hassle and spilling...
b) That KIND of faded, but it's still true - I have however decided it's outweighed, and I'm buying more tanks
c) There is a flavor improvement. A stock carto tastes better than a stock coil - and I don't enjoy wrapping coils...
d) There is a BIG difference in the ability to "keep up" - a Protank, even working properly, can't wick enough juice for repeated "big hits". A carto can.
e) For the same reason, a carto is OK at slightly higher voltage. I usually kept Protanks under 4 volts (with coils running typically about 2 ohms). SAME resistance, a carto is OK at 4.2, 4.3 no problem - which lets you hit harder, and bring out more flavor.
f) Less trouble at the back end - once you prime a carto and fill a tank, you're good for a long time. The tank's bigger, and the carto's good for...well I haven't figured that out yet - maybe a week? Maybe 2 weeks?
I think it's worth it just for the flavor.
So now I'm collecting tanks (and I still have ProTanks in unopened boxes- might have to sell something soon).