Maybe they will merge both subtokens in a later step.. I thought I read in their roadmap that they will unify both BFG tokens.
You could also use them for the auctions, but these last couple of days it is very difficult to reach the top 10. Sometimes you need to auction 20-30 BFG (TRX) subtokens to win 1-2 TRX.
The auction board is very tricky only the top 10 bidders will have a share of the stakes so it's better to bid in the last seconds I won some Tron doing this and I only bid 1 BFG higher than the last one to make sure of a good share and I am in control of my position, there are times that bidding are huge and there are times bidding are small so plan the best time to bid.
Actually, that's what I noticed also. Better bid for the last few seconds because if you will bid early, you will most likely not get any share. And also, the amount you will get in staking is getting bit lower. Hope the value of their token will be worthwhile when they list it.