battery is better than 910, it's lighter and current run pace kinds works, sort of. Can't do footpod SPEED preference. HR for openwater with MIO. More poo swim stuff (better?? prob not really), does all the smartphone stuff. I got through 3 or 4 910s and i'm on my second 920 already. I like it apart from the colour.
Never liked the GPS unit armband of the polar RCX3 and confess to not having tried the Scosche.
Scosche uses a 3LEDs system which, combined with the position, is probably why it is more accurate than others that have 1 or 2 LEDs. The 225 has a 2 LED system and so will probably go a 'bit funny' at higher HRs like the others seem to. The truth will come from wearing it I guess.
And there are quite a few places on the net where you can see the different physiological adaptations that each occur when training in different HR/pace zones.
An individual's target race distance would dictate the amount of and timing of training at each level.
I think one of the areas that we use different words for is 'easy run', which I really don't like. Personally I would take 'easy' as a recovery run whereas other might see 'easy' as being a bit faster. A recovery run is too slow for improvement IMHO.
Further to the point on injury, with which I agree, training frequently at an 'all out' level will also increase the required recovery time. In that recovery time either you can't train or your training is impaired. Perhaps if you are training 2-3 times a week that won't be too much of a problem but more than that it probably will be especially if you are a bit older and required recovery times or greater.