Herman, I bought a GM3 when they first came out, on the first trip I found a nugget that was just over a 1/4 ounce. I could have found it with any gold detector. The GM3 has the same background noises but worse, the coil still gives of false signals when you hit brush, the signal booster will drive you crazy, and the frequency control does not work like they claim, you still have to stay away from someone else using a whites. After the first trip with the GM3 I and my friend made about 6 more trips with the GM3 and walked about 25 miles(there is a mineral out their that is in pods has a fushion type crust, feels like sharkskin,is black heavy, non magnetic, except for a pieces the size of coarse sand, and super hot, sounds like gold, I think it's Chromite.)Anyway we came upon a deposit of this stuff, and the GM3 would not pick it up. this mineral is as rare as the gold we were looking for. So when I got home and made some test I discovered that I could tune out gold and this mineral, I sold my GM3. The SD2100 is a super detector,you may run in to problems if you are around military installations at times when they have something going on. The newer SD2100 have quite a bit more sensitivity then the first models, so thunder storms or certain military signals can cause a threshold that sounds like a bunch of birds chirping. It's to hot where I go so I really can't tell you any more about the SD2100, The only time I got to use mine it started snowing, so it got wrapped up quick. If you can Justify the cost or know of a hot spot go for it and make sure you get a 11 inch mono loop it's the hot one.---------- Just my opinion, Mel.