Thanks guys, that's a lot of info!
I've been reading a bit more on Garmin Edge units and yeah, the 500 seems like a very solid unit! Is the newer model 520 much better or no major benefit in my situation? Getting a used 500 for under £100 surely is a much better deal than getting a new 520 for £200 right? (plus it's well above what I wanted to spend).
What is the rate of update for the cadence and speed sensor in the Garmin Edge 500/520? I have also seen the Garmin Edge 25 which is ANT+ compatible and can too export data, but considering I could get a used 500 for the same money or less it's probably not worth... And who knows how fast/slow it is taking cadence/speed measurements... Has anyone used/heard of it?
In terms of the actual sensor you're right Carleton, keeping a record of all the gears for every single effort so I can then calculate speed would be too crazy. Hadn't thought about that!
So yeah, will get both speed and cadence meters. The latest one from Garmin has extremely good reviews so I'll probably go for that one. Like you said Poppit an extra benefit is that the speed sensor attaches to any of the hubs, so no need to get anything to the fork and front wheel. That is using normal wheels which, which I am using (at least for the time being, and probably for quite a while because I have no plans on getting disks/3-4-5 spoke wheels any time soon).
That being said, is there any benefit from the conventional magnet "ticking" cadence/speed sensor over the internal accelerometer style of the latest from Garmin? The old GSC-10 seems to be out of stock every by the way, Queerpunk.