Younggun,
All Metal is great for picking out the goodies next to junk. If that is the reason you are using all metal that is fine, but when I read posts like yours (and Bob why all the time?) I wonder. I had a lemon SE that would false high coin tones off iron badly (in both directions). I struggled with it all last year and finally sent it back for repair. My solution, to use the darn thing, was to run in all metal with ferrous tones. It worked good that way but I had to watch the screen much more than I like. Plus all the signals wear on you after a while.
From my experience using the oringinal Explorer and the EII, in conductive tones with IM set low (less than 1/4"), only the occasional bent nail will give you a good high tone in two different directions (initial sweep then turn 90 deg. sweep again). Usually on the 90 deg. sweep the signal will null right away (on iron).
I have a sneaking suspicion that folks are having the trouble I had and are resorting to all metal in order to compensate.
ML did me right and I think my SE now works as good as my EII. I am still evaluating.
I use all metal in fields where there are high concentrations of iron trash (hoping to hear that goody next to iron). I dig anything that is not a low iron hit. Yard hunting though, I don't think you can beat conductive tones with a tiny bit of IM.
Just FYI, HH - BF