First: Having a wrist strap will make the product more unique and will drive sales.
As for instance the 625XT can be used for runners that occasionally bikes, the 580P can be used by bikers that occasionally runs.
I have used it while running too, to get better elevation profiles. I also like the big screen, the 625XT is too small for me. The 580 uses the big screen better too (no black borders). For me, the height/width could be bigger.
However, the current design will not be a 5 star product. The device is simply too thick to be used comfortable on the wrist.
I tried limiting the height using a ziptie to tie it to the velcro, but it is still to thick (and not reliable enough to use!). See picture:
Drilling holes in the socket (also turning the device) and use threads to tie the velcro will be better, but I do not know if it is usable.
I may try it in the
Another issue is the device software. Distance calculation seem to be optimized to (surprise) biking, not running. This is another reason to have optimized run/bike modes.
The GPS reception in my pocket may not be the best, but it will not be much different to the wrist. The antenna seem to be less sensitive than wrist devices (sats need more time to synch for instance). Not a problem biking as I have more preparation time there, but it is annoying when running. (The 625XT synchs while tieing shoes).
But if the considerations are considered for next product, it could be a killer product.
In my opinion, the low-end GPS market will get very serious competition from smart phones, at least when wrist companions are more common. The features need to be unique.