I did my first one yesterday, at least the first one worth mentioning. I previously had a Polar A5. I certainly like the extra functions, but the actual HR part of it, chest strap..etc I likedbetter on the A5. It was smaller, almost NEVER got any inteferance, and seemed to pick up faster/better. I'm not sure why they had to make the sensor bigger.
They also have a "wearlink" transmitter that's almost nothing but a strap, which I'll probably get. I have a feeling I'll like that one better. I got the cadence sensor also, which has proved interesing. I thought I was pedaling in the 70-80 range most of the time and I'm really in the 90-100. I really didn't expect that.
The software is "okay", but I'd like to be able to customize it more....I don't know it real well yet though. I'll probably go ahead and get the power unit relatively soon, that's the main reason I upgraded anyway.
All in all it has some quirks, but the pros outweigh the cons as far as I can tell.
John