I use the SQR with the Tour Slim (although slim only in Carradice terms, I still had shoes, helmet, clothes, etc in there the other day) and never had any problem with it feeling secure but the SQR Tour bags are designed for that mount with a metal frame on them and a base to them.
Personally the convenience of clipping them on and off (I have a couple of bikes and a smaller SQR Glentress which is a great bag that they've discontinued) trumped the classic design for me.
I use the SQR with the Tour Slim (although slim only in Carradice terms, I still had shoes, helmet, clothes, etc in there the other day) and never had any problem with it feeling secure but the SQR Tour bags are designed for that mount with a metal frame on them and a base to them.
Personally the convenience of clipping them on and off (I have a couple of bikes and a smaller SQR Glentress which is a great bag that they've discontinued) trumped the classic design for me.