So, let me get this straight, you wanted to send roughly $6 and they wanted to charge you $6 to do that. Wow, where do I sign up for this kind of rape fest?
This service is not meant to use for small transactions logically (you have ViaBTC for that) and as I already mentioned, the fee that BTC accelerator take is based on the current btc price, TX size and some other factors.
Transaction accelerators with no fees tend to have hidden agendas since there's no economic reason for them to provide that service when they could make more money. In ViaBTC's case it's to argue for BU which they most likely believe would make them more money in the long term.
Plus ViaBTC is already pretty saturated, their service isn't going to be that fast when they're only including some transactions in the blocks that they mine.
Fee accelerators shouldn't be free because it makes people just try to screw over other people who actually need the accelerator because they did something wrong with the transaction.