Update, but it's not good news I'm afraid.
The new Montana worked well for eight days, but yesterday is froze. It wouldn't switch off, so I had to take the battery out. Switching back on again, it froze again, and repeating just gave the same result.
I connected up to my computer this morning and found how to sort it, by deleting the GPX folder and doing a master reset.
All went well, and the Montana came on fine and didn't freeze at all.
However, there is zero satellite reception. Not a show of any bars at all despite leaving it outside in clear view of the sky for an hour.
I phoned Garmin support and they got me to do it all again and check for satellites again. Also to do an auto locate to clear any old satellite data. Still no joy at all.
I will be sending the device back for another replacement!
All to be arranged as yet, and doing the rest by email.
Mick.