Not using that one on my 1250RT but do use the Givi ST611 tanklock bag, small but works for what I need it for.... I came to the conclusion that anything bigger was going to cause issues with steering lock... even this dinky little 6 litre bag does come into contact with the BMW aux lights switch on full left lock...
Doesn't cause a problem though.
Detaches and goes back really easily.
HTH