Don't have the uMax, but do have it's older brother the Golden Sabre. It also has a preset ground balance, and for the most part, works well everywhere. There are however, a few areas in Manassas, Richmond, and South Central Virginia, where my other machines did considerably better because I was able to adjust GB. BUT. .. .most of these sites were camp sites or battlefield areas without a lot of trash, and I'm digging everything that hits with discriminator minimally set, or All Metal. When I use the Golden in park areas athletic fields, it does just fine. . . ..in some cases excels. ...and because many of those areas do have a lot of trash, the notch becomes a handy filter to reduce at least the pull tabs strewn over the area.
The ED-120 discriminate, narrow or wide notch, and now multiple tone id's on the newer uMax, are significant improvements over the older versions. If you're primarily a coin shooter and hunt a lot of potentially high trash areas, this might be the ticket. . ..ground balance or otherwise.
Hope that helps - HH
-Ric