I've recently bought an Arkel rack and bag to use on my Xootr Swift. It would not be strong enough to use on a fully loaded extended tour but for general riding and commuting it's fine. It has a quick release bracket that clamps to the saddle rails and a soft rubber grip that wraps around the seat post. It can be fitted and removed very quickly which is great for folding as the Xootr needs the seat post to be clear for the fold.