Have you looked through all the and product FAQ's at Sigma's site?

I'm sure they work well for many, but I'd never spend more than twenty or so bucks on their products as Sigma has little product support options and no community forums that I'm aware of.

As for sensors that use wheel magnets, I've used them for years and still do. Simply because I've never had an issue with them on either of my bikes. Nothing against the newer magnet-less sensors, it just makes no sense to throw away old for new.

If you decide to spend more money on another product, go to the manufactuers website and see what your support options are. Lack of a community forum where I could ask questions to other users would be a negative.