The Vaude Trailsaddle II consists of a very robust mount and a pack sack with a total volume of ten litres. The construction is quickly attached to the seat post and the seat stays and is very stable. The bag offers a lot of volume, but unfortunately has no air valve for more effective packing...

... Vaude has attached tabs on the top that are supposed to be used to secure additional luggage. However, they are so close to the saddle that you would bump into them with your rear end. What is missing is a tab for attaching a rear light. So you have to attach it to the rear strap - where it can easily slip.