So the Polar computer does everything the Garmin ones have been doing for about 3 years! Although with Polar as usual everything is an optional extra.
You get the cycle computer with free heart rate monitor for: £278.45
The cadance sensor is an extra: £38.66
Power sensor is an extra: £273.55 (or an extra £185.95 if you buy it with the cycling computer)
The GPS sensor (same receiver as Edge 305) is an extra: £121.85. Plus changing/charging the AA battery every 30 hours.
Not quite sure where BIKEmagic came up with their price, but I presume the Polar price on their website has dropped. Still the features mentioned in the review (excluding power sensor) currently cost £438.96 Or you can get the vastly superior Edge 705 with GPS, basic mapping, heart rate and cadance for £274
The website description does not mention if the PC software is the free trial or full version of ProTrainer 5, but the full version is another £50 it also doesn't say if the IR reciever for data transfer is included! Buying one of these things is such a mission of guesswork... although to their credit the last Polar watch I bought did come with all sorts of extras like this in the box even though they were described as optional extras in the review.