This isn't at all a detailed comparison, but this sub-forum seems to be right place to put it. I'm pretty sure these devices are no longer made for any detector models, but it might help someone thinking of buying a used one. I bought a used FX-1 (for Fisher F75) recently. I did look for reviews and found a few, but unless I read too fast those didn't tell the key features (particularly minuses). This is not meant to be an overall review like you'd find in a magazine. The other reviews you