In reply to ams558:
Hi Alex,
I've used one for a year or so and it does basic HR monitoring perfectly well, it has easily replaceable batteries, and is a reasonably rugged unit (but face is easily scratched).
The M5 is fine, but it's expensive for a basic HRM, and is limited in functionality compared to models priced only a bit more. If you need a 'focused' HRM with plenty of data vis-a-vis R-R intervals, EPOC, training effect etc., look at a T6c / T6d, or at least a Quest. If you don't need that, you can get a more basic HRM for a lot less.
HTH
Luke