I thought that nothing would replace my Polar RS400 HRM, but the M200 has. However, for accurate heart rate monitoring, I use it with a Polar chest strap and H10 transmitter also bought throgh eBay. The GPS is good and downloads to Google Maps, although altitude can be a bit inaccurate. Comfortable to wear even on a Concept 2 where my wrist tends to enlarge. At the right price this is a good buy.
Heart rate seems to take an age to stabilise. I have had issues with GPS data and attitude not synchronizing. This was an enforce purchase as Polar no longer offer support for 31st December for the RC3 GPS with HR.