I was in exactly the same boat as you when I was shopping for a bike computer and while you can get away with a CatEye computer for about $50 or so, there wasn't any way to get the data off the unit. Or use ST's mapping facility and analysis software either. Off the top of my head I can't think of any bike computer that is downloadable and gives as much info as a Garmin.
As a result, I bought a 305 last year and used it as a stand-alone bike computer. For Duathlons I had great results pairing it with the 301. You get a double download into ST though, but you can just combine the workouts there. I wear the 301 HRM throughout the race and just use the 305 for cad/speed/elevation.
On the trainer, the rear-wheel speed and cadence sensor is easy to set up and is wireless to boot. You have to turn the GPS off otherwise your wheelsize is all out of whack but you know that for Garmins indoors anyway.
Shop around and see what grabs you though - if you can live with the non-downloadable stuff then any bike computer will suit. The main thing is that you want a computer with a REAR wheel speed sensor if you're going to use it on the trainer because that's the only wheel that spins. Unless you're riding rollers...
If you're still set on the 305, PM me as I'm selling mine cheap because I bought a 705. I'm using all the 305 components so you get brand new HRM, bike mount etc. I didn't get the cadence/speed sensor though so you'd have to get that separately but that's pretty inexpensive. I want someone to take the 305 off my hands as I'm trying to save for a Triathlon/TT frame and boy, those things are pricey.
In God we trust, all others bring data.
- W. Edwards Demings
If God invented marathons to keep people from doing anything more stupid, the triathlon must have taken Him completely by surprise.
Specificity, specificity, specificity.
The plural of "anecdote" is not "data".
- Frank Kotsonis
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