Jake said:
is the tesco one wireless too? dont really need anything too grand, i'm not planning the tour de france just yet. Your new one sounds pretty cool
Nah, the Tesco one is wired. It's not a huge chore to put on, though: there's a little magnet goes on the spokes (front wheel), a sensor you cable tie to a fork leg, run the wire up to the bars and into the computer which has got a multi-position mounting thing that goes on the bars. Oh, you need to tell it your wheel circumference as well.
They all work in pretty much that way, even the Garmin has a sensor for the wheel .. it works out your speed using the GPS but uses the sensor as backup. The wireless ones mean you don't have to trail wires round the bike, but can be prone to interference so I hear.
I've not got either the new Cateye or Garmin one yet .. still trying to decide which to get, in time for Christmas!! (I feel like I'm 14, not 40!) In fact, there's a recent-ish thread in "Accessories and Clothing" that I started asking for opinions on both. And there's loads of threads generally about the merits or otherwise of various makes and models.