I'd like to report great success using the Carry Speed filter ring and a 46-49mm step up filter. Many weren't pleased with the CPL quality and/or that lack of threads to use their own filter. Well you can simply take it apart, get a $3 step up ring, 46-XX of your choice and some super glue and have just what we hoped this product could of been all along
As you can see, the little outer lip on the red part just happens to perfectly fit inside the 46mm male outer thread.
http://img690.imageshack.us/img690/4773/cheesy1.jpg
I added a few spots of superglue to the magnetic ring itself and sandwiched it back between the red and black parts, and then added some glue around the lip of the red part and stuck it all together.
Now I've got 49mm threads on the front I can use anything from my filter collection with and that sticks on/off with the built in magnet. The little metal part that sticks to the front barrel is so slim you don't even know its there when your not using a filter.
I'm seeing no vignetting even with 2 stacked filters at 28mm equiv as well.
http://img525.imageshack.us/img525/1733/filtersf.jpg
All and all I couldn't be happier with this product!