Thanks for the info, all.

I have a question about magnets. I solved one magnet problem by adding a Home Depot neodymium(?) magnet to the one provide by the packager. That solved the problem. Does that work for these types of sensors? (Of course, magnet-less sensors offer a different and perhaps better solution.)

My budget was originally $25, but having read complaints about so many of the offerings, and having read your comments, I've upped it to include the Wahoo combo or just the Wahoo RPM cadence sensor or some other offering that has a price which implies rigorous QC. Foolish, I know, but hope spring eternal. :-)