I use a basic expedition bagman support i.e not the quick release one with an 18 litre longflap carradice saddlebag, can’t remember which model.
It works fine. Bear in mind you need loops on the rear of the saddle for the bag straps. Not a problem if you have a Brooks B17 or similar. Otherwise the QR Bagman does away with the need for loops I think. You also need about 20mm of parallel saddle rail showing behind the clamp on the seatpost to fit the bracket.
It is well made and doesn’t rattle loose or anything. If you are using it on a road bike make sure there is sufficient room for the ‘drop’ of the clamp so it doesn’t end up sitting on the mudguard or rear wheel.
The bike looks a bit odd (to my way of thinking) with no bag fitted. Doesn’t bother me though as it is on my commuter and so the saddlebag is always on the bike.