I ended up being less than impressed with my nimble nano (I got a regular, and a super) -- they just don't have much "attraction". Maybe there's some variation and I got a dud pair?
I've got a small mag-float knockoff called a "twister"; not sure where I picked it up, but it does a much better job than the nimble or the small magfloat on my BC29.
Still, for the front corners, nothing works as well as getting my hands wet every few days and wiping it down with a scrubber pad... I also use a "razor blade" style scraper on any persistent coraline at the same time.