I have had one in mine for about 3 weeks now with no troubles. I just have to make sure that it goes in with the rounded side down. As for "really working," I believe they improve the result, especially on fast stitching. In tests with and without, my high speed zig-zag stitches were more uniform with it than without. Couldn't see any real difference on those done at slow speeds. I haven't done any embroidering since it's been in, but I'm guessing it will help based on what I saw with the zig-zag stitches.

Jan in MD