I've used Antti's patch for a month now, maybe a dozen runs and bike trips altogether. The delay is reasonable, connecting to the belt takes a handful of seconds and the heart rate is displayed after another 3-4 secs. I've had no problems whatsoever with reliability.

We don't understand the protocol well enough and the patch probably won't work for all users. My Polar uses 0xd1 as the key instead of 0xf1. I added another switch-case and now it WorksForMe(tm).

--Martin