I have the Polar 710i and must say that after 6 months of use, I wish I had a PC that could download the readout's. The calorie and fitness test functions are nice to have, but a cadence function is more important.
http://tdf.polar.fi/tourdefrance/heartrates.html Polar have some readout's from the Tour. This has really excited me about getting a PC so I can download my sessions.
Being able to compare my heart rate at the top of a climb with previous rides is a great way to see if my training is getting me fitter or have I reached a plateau.
The cadence and PC connection are a vital part of assessing performance. Having said that, I should point out that I am very analytical and love number crunching.
CHEERS.
Mark