This is good if you are using a lot of filters. You no longer need to remove the mount. I don't store my camera with this mount and cover.
This is perhaps the only way to protect your lens when using the Cokin filter system without a filter inserted. It seems very well made, although it takes a wee bit of effort to seat it properly in the Cokin holder. If you're shooting a lot and switching filters left and right, you most likely will not use this very much. On the other hand, if you hit a stretch where you aren't mounting filters in the Cokin holder, having this handy and using it will protect your camera lens.