Yep. This method really isn't current. Jetmouse "retired" a long time ago. (He was a Genius.)

There are always more layers or protection added, and as Cnfhbr mentioned, Garmin added the GMA file necessity for unlocking.

I believe the most recent unlocking method was gimgunlock, but it doesn't work with some of the newest device firmwares. Particularly the Marine MFD units.

It's a cat and mouse game and at this time, the Cat is winning.