same here ana... i've been looking at the a2-t and a2-tm for a couple of days now. i'm getting the p+10 sometime next week and i still don't have a topper for it.
from what i read, bulli's are 'hard' to set up. i don't mean difficult to build or w/e, but the difficulty seem to stem on proper wicking. i'm also concerned with leaking issues but so far, i have not found any complaints with leaking.
i guess my main concern would be flavor and wicking and people say that the a2-tm seem to produce slightly better flavor (when properly set up) than the a2-t. no one knows why since the innards are the same and the only difference is the size of the tank. aesthetic wise, i'm more partial towards the a2-t since it has that nice taper at the end, but like i said, people seem to say that the a2-tm produces 'better' flavor from their experience. also, a2-tm does hold almost 2ml of juice, while the a2-t holds i think 1-1.25ml.
oh one more thing to add from my research (or lack thereof lol), the ego tank type A (the one used in a2-t) seem to be more widely available (i THINK it's the same type super T. has on sale... 1.50 for a pack of 5, but i'm not exactly sure) and have less complaints than the type B (the one a2-tm uses). this is anecdotal as i've only really found one site that has replacement type B tanks that included customer reviews... from the 4 or 5 reviews, 3 noted leaking issues iirc, but those could be user error as well so take those with a grain of salt.
as of this writing... i want to say that i want to get the a2-t over the a2-tm but then i'd be lying... i'm still lost tbh LOL.