AEG to GBB? Huh? Well... GBB`s are great, but... they`ll sell kit probably without magazines (or with accordingly higher prices), and taking under consideration cost of the rifle... Uff, if everything together (I mean Tavor plus GBB kit + Mags) will cost less than, lets say, 800 euros MINIMUM(gas mags are Dear - with capital D in front of it, and GBB will be dear - I can bet, + gas mags are not taking much bbs, so you need at least 5 of them)...
And, as well, I`d like to say that Ares is using CG`s licence to produce TAR (so Ares TAR 21 will have fo 99% markings). TSI - probably not (if they will have that - will end up in court again...:-/).
Taking under consider high costs, there is as well issue with realiability with GBB`s...
I would say, that I preffer to get Ares TAR21, that taking TSI version, than, after few months (if TSI ver. will have good reviews, and will be worth its money), I`ll consider TSI`s GBB.
I`d like to say as well, when I`ll buy and GBB rifle - ebaybanned is selling GBB M4. for much much cheaper.
But thats (of course) only my personal approach to the subject :-D