I use this with a Garmin Edge 305 on my road bike. Cadence works great and seems very responsive to changes in RPM. In low GPS coverage (heavy tree canopy) the speed sensor keeps my ride distance accurate within reason. I did have it loose synchronization with my Edge after I washed my bike. I thought I'd killed it. An email to Garmin was pretty quickly responded to with instructions on how to re-sync which resolved the problem. Waterproofing seems very good and it is a simple effective design which will even work with a trainer since it reads the speed off the rear wheel.

Works well on road bikes and stiff-tail mountain bikes. For full suspension mountain bikes, which I use for commuting, the mounting does not place the cadence sensor in the proper position for use. There needs to be an auxiliary mount for fully suspended bikes.

I was excited to get this to go with my Forerunner 50 but the bottom line is it doesn't work well at all.
The sensor stops sending data relatively quickly, like while waiting for a stop light, once you stop pedaling and does not start back up automatically. So I've had quite a few rides where all data post stop light was lost. On top of that the arm with the speed sensor broke after 5 months and now the thing is useless, won't even read cadence even though it's the speed sensor that broke.