I got a 645 last year for £200 just as it was being discontinued. It’s a generation behind the current ones and Garmin don’t push any new features to it. It does the usual running GPS + wrist heart rate stuff, plus a whole bunch of other things when worn as a watch, like step tracking, sleep tracking, general HR tracking, HR supersampling things for stress measurement, and also works with an accelerometer pod for stride analysis stuff and power data calculation when running. It also streams music over Bluetooth.
It goes a lazy week or so between charges. Less if I exercise, and much less if I use the audio stuff. I like it.
I think in Garmin’s current running range the 245 does most of the same stuff with a newer heart rate sensor. I’d buy similar again, and would consider a deal on a 945 for the added cycling functionality (though this one does most things except for power meters).
Gus