I think it depends on what game(s) you intend to play. The support for GW stuff (Warhammer and Warhammer 40K) seems to be pretty solid, but other games systems may suffer from less frequent updates/corrections/fixes/etc.
I have the V2 version but I haven't upgraded to V3 because Army Builder only works on a PC and I switched to a Macintosh.
For GW players, it can be fun to sit there endlessly reconfiguring various army lists, and some tournaments prefer that you submit army list in the AB format.
One drawback is that you do tend to lose some facility with doing army list math in your head, since AB automatically totals up the points for you.
Overall worthwhile if you don't mind the PC drawback.