Well, there are some similarities but blood doesn't flow through a Watchman after the first few weeks. The Watchman is designed to encourage your endothelial tissue to grow over it and completely seal it closed, whereas the carotid filter is designed to remain open and let blood pass freely.
Incidentally, filters like that have existed for many years. The difference is they were used in the venous system to prevent DVTs. I think using them on the arterial side is what's new.