The order was promply filled as promised and arrived a 3 days. The merchandise was new and in exdellent condition. I have not yet had time to use it seriously.

True, this attachment blocks the pop-up flash of the s1-is, but I use an external strobe with a Wein photocell trigger on the bottom to compensate indoors. You can mount it on a bracket with the camera, or handhold the flash to avoid red-eye, bounce off the ceiling, or angle the light from the side.
The Wein attachment works with any strobe, make sure you get the one that ignores the red-eye reduction flashes (yeah, it's that good!)

If you are serious enough to use a camera of this quality, or the new s2, this is a small annoyance to get the wide angle capability this adapter offers.

Wide converter lenses normally make sense to be used indoors where space is limited. But the WC-DC52a can hardly be used there, because its big diameter results in a very big shadow on each flash-lighted foto (in addition the Powershot S1 IS doesn't support external flashlights).
So buy this lens only when you want to use it outside!