The IBKR commission rate seems really off. I just spoke to TD Ameritrade - they said they will start offering MBT very soon at $2.25 per side which is nice.It's a rip-off! Try to buy one bitcoin with micro contract and commission is $75 (10x 0.1 BRR "MBT")! However full contract with five bitcoins (1x 5 BRR "BTC") would cost you just $15.
Try to buy five bitcoins with micro contract and you will go broke ($376 buy, $376 sell).