The Focus S corners are rounder, the camera cut is different, the front sensors and back speakers are on different sides and the Focus S has a physical camera. So a tight fitting case will not work.
However, since the dimensions are similar (67x126x8 mm [Focus S] vs. 66x125x8 mm [Galaxy S II]) a flip style case that clips in on the sides may work.
Gadgets should show up in the all apps list, not in Settings. If it doesn't, there's a few other places where you might be able to find and uninstall it:
Settings → Apps → Apps & features
Device Portal (see this answer for instructions on how to use it)