Sportsbet.io is quite a big BTC bookmaker, I know a couple others that use it and they never had issues making withdraws. I prefer not to move too much BTC around with the costs that are linked to it. I also keep the minimum I need on Sportsbet so unless I get in a big upswing I won't be withdrawing any time soon. They also ask for KYC if I understand it correctlty and I tend to be lazy with these things. Good luck if you end up using them @minimining !