Managed to load these maps on my Montana 610. The downloaded maps worked in Basecamp but were locked when copied to SD card. Used gimgunlock on a PC to unlock the maps but was then faced with authentication error. Not wanting to run the risk of patching the Montana 610 firmware, used ImgTool to set the Code Page of everything to 1252, copied the resulting files to the SD card. Maps are no longer locked and are authenticated. I have not experienced any problem with using the maps and the quality is slightly better than that using the older Discover GB V4 maps I was using previously although they are still not particularly up-to-date. Not really a problem for hiking.
Just a couple of comments. I am not sure about the 1205 code user bonefenix mentions and I did not try it as I assumed it was a typo and 1252 worked for me.
Be careful with ImgTool dowloads. I found several versions which were riddled with viruses! The link to ImgTool1.9.29 on this site appeared safe when I downloaded it. Avoid other versions and scan every downloaded file for malware!
Moderator NoteImgTool has its own thread where this is covered
User bonefenix also mentions a 100m error when using these maps. I have tested one of them in a area I am very familiar with and can report that there is no systematic error in position with accuracy of better than 3m with my Montana 610. I would therefore suspect any error is to do with his GPS unit rather than the map. I have no experience with Garmin watches (people must have better eyesight than me if they can use mapping on a watch).