I watched a demo of the Gold Monster, it has a great sensitivity to small nuggets! I watched 2 fly specks pulled with it. As for a need, it can find very small gold and also it can find gold in matrix that a PI will not hit on, again it was proven to me in a demo. 1 9 pound stone with over 7 ounces inside would not sound at all with a PI with any coil or setting. The GPZ picked it up as did the vlf's. The advantage of the Gold Monster over the GB2 is the Gold Monster sets itself, no adjustments. I plan on hitting some areas with tailings piles. The Gold Monster is perfect for those patches.....again no gpx is good. I have a GPX with NF Evo coils. My plan of opration is use the Monster to find a patch, then have the wife hit it with her SDC 2300, then go back over it with the GPX for deeper targets. Just my opinion....