hi JJ
I agree with old Cal
i have a GM2, & 3 and found them to be a very good MD, found many of tiny nuggets, however with that being said a lot of my buddies all seem to have a hard time with the ground balance, because of the fine and course knobs on the unit. also they would have a hard time on heavy mineralize ground ( need to turn the gain down ) losing targets, needing to manually ground balance all the time.
The GMT does most of the work for you with preset and the a couple of pumps up and down with the loop your balanced and ready to find nuggets, GMT also works great on heavy mineralize ground. GMT can do the ground balnce for you or you can do it with it in lock and with a simple press of a thumb your balanced agin
if you can i would try to save for a used GMT, just my two cents worth
2cmorau