In reply to jlury:
I use the 5X, really impressive watch though the map function has been largely redundant for me. Used a couple of times whilst out walking/ hiking where it has actually been quite useful. Biggest downside is that when under layers its a bugger to get at, so the phone or map is an easier option.
For coordinates or OS maps there is probably a widget/app or somesuch you can install that just punches out a utm grid ref. It seems (having just had a quick fiddle) that there is no immediately obvious option for this with the default map viewer.