Just checked my accounts and I have spent close to £1000 on HBC since starting to use it in April 2017. I always top up the maximum amount to get the biggest bonus, but I think it clearly is a financial sinkhole - unless you can afford it!
Looking back at how much I've spent on it in such a short time frame, I think I would rather have spent the money on something more real like sessions (that I have yet to try!)