I have one question, Is this legal, is the bookmakers close my account, if they know I am doing matched betting...
It's legal, and if you do it well the bookmakers will actually like you. Since you are losing on the house that gives you the bonus.
The problem is when you win there and normally withdraw after completing the rollover. That way there might be a chance that they lose money with you.
I used to do it with fiat, but I never find bonuses with bitcoin to do it as well.
Are you doing it with bitcoin sportsbookers? (like direcetbet etc)