Well, I went and bought them and for anyone interested here's my opinion of the CS4 panniers. These are really well put together bags, with strong stitching and good quality leather. The pannier liners are strong and it looks like the construction should keep their shape well. As for the locking mechanism this is really good quality. the mooting brackets fit perfectly and have a good finish and the locking quick release system seems strong and well made also.
They took no more than 15 mins to fit, mark up and mount the bags. They are well clear of the springs and sit well on the bike.
Off for a long ride tomorrow so we'll see how they fair after that.
Red_SE_1600, thanks for your input. It was much appreciated