I too have the 6mm Festo ball valve fitted.. Just be sure not to use it with Tygon tube. Only the original Festo 6mm Tubing. It's no way near as flex as Tygon, but its the only way to ensure a solid seal each time. I also change mine from time to time as you can see the marks where the claws inside the connector grab onto the tubing. Not sure how necessary this is, but it gives me that warm fuzzy feeling inside
Regards Al