I've always used Polar HRM watches but got fed up of having to send them back or buy a new one when the watch battery ran out.
So I bought a Suunto T3C watch - something of a disaster! Not intuitive to use and unreliable.
When the Suunto T3C finally packed up I looked again at Polar and delighted to find they now have user replaceable watch batteries.
I ordered the FT40M because it had all the features I need which in order of usefulness are:
1) Measures heart rate ( rather essential! )
2) Comfortable to wear chest strap
3) Calculates how many calories have been burnt
4) Can connect to the PC and download data ( needs optional Polar FLOWLINK accessory )
5) Has fitness test built in
This is all I need really as I just use the monitor at home or in the gym with the aim of losing weight and keeping fit. Other more expensive models have options for GPS, extra tests, strength training programmes but for me these are not likely to be used much.
Been using it for a week now and picks up heart rate very reliably ( unlike the Suunto T3C ). Calorie counter is great for motivating me to exercise. The PC download is nice for tracking progress. The fitness test is probably something I'd only use infrequently but it tells me I've very fit for my age and who doesn't like compliments!