Shorty packs are allowed but not of much use as usually you have to add weight as it is to get to the 1550g min.

I have a pair of promatch shortys that feel pretty punchy but are a big pain to balance every time. Honestly I have been the happiest with my Gen Aces for VTA. 4 packs all over a year old and are raced week in and out in VTA and they still feel great (and all 4 cost less than 1 battery from another company...).