I have the 405 Forerunner It's really good I use it on one of my bikes instead of a computer.
However it is not that accurate if you stop and start a lot as the auto-pause takes a second to start.
make sure you give it five minutes before you start to locate the satellites as you will need to turn the gps off to save battery between uses.
plus the longer you give it before the ride the more accurate the gps will be, so if you go into trees you still get a signal.
It is also good if you park somewhere save the Gps location. Then just bike in any random direction then you can use it to guide you back to your start point.
if your keen on training (which I'm not lol) you can use the training partner thats built in.