mmmm
Firstly, I would not get too excited about the Gibraltar regulation. They are happy to take fees and are sod all use if you have a dispute with the book, plus for many years share bucket shops of various sorts have happily operated there.
If Mansion wanted regulator credibility, it should be based in the UK mainland like Betfair.
I am suspicious of this book. I am not sure why exactly, some of my friends who can generally sniff out a scam book are happily posting up cash there. I may be wrong, but something just does not feel right to me about this lot.