I only tried it once, and just didnt trust it either... I think it would be okay if I was just looking for coins (I get the feeling that is what is supposed to be for), but if all the bigger gold rings are in the pull-tab range, then wouldnt it disc them out too?
Just FYI for any MXT users that may not have read the MXT book, I got a tip on it that is FANTASTIC!...
I will often get .01-.10 hits that after a couple sweeps jumps from that to .25 and .50, then back to .01-.10.... Seemed it was always a bottle cap, but I didnt want to miss an old coin, so I would dig them.. The "Tip" says to sweep target, but instead of going over it, just barely let the outside edge of the coil get near the target, and if it is a cap, it will show as an Iron VDI... Works like a charm, and now every time I get that signal, I try it, and sure enough, it shows as Iron.. It has saved me hundreds of digs..
Book says something about the mix of iron and steel in the caps, and it confuses the computer.. Give it a try, you will really appreciate not having to dig those stinking bottle caps..