I've done the airside transfer QR-BA and it is very easy, with a personal security check and your own bus, so it isn't a problem from that perspective. There is a button to press near the security point and you wait for someone to come and check you and put you on the bus. It delivers you to the non-Schengen gate area though, which is after passport control and with no access to the lounge or any refreshment or shopping option other than a vending machine. When we did it, we had a fairly long layover and luckily managed to knock on the window and negotiate our way through passport control backwards or it would have been a very boring few hours.