AuDuke,
The TDI, in pure PI mode ( ie, ground balance OFF ), will be just as good if not better than the DF. The thing that puts it over the top, is the ability to use the ground balance feature as a type of discriminator to eliminate iron. You CAN coin shoot with it via setting up the GB and using the conductivity switch. Granted when setting the unit up that way, the ability to get gold and nickels is also eliminated ( that is, when you set it up to totally eliminate iron and low conductive targets), but you can silver/copper hunt in iron laden areas with no problem. Depth suffers a bit in that mode, but that is compared to the pure PI mode. One good thing is, in that mode, it can also eliminate a lot of the beat up zinc pennies that ID/hit in the gold range.
In addition, there are a lot of coil options for it.
The only downside is...it's not waterproof. So if you are going to be hunting a lot of salt water beaches and wading into the surf, I suggest the DF for the simple fact that you can give it a fresh water bath after hunting without any worries. And you don't have to worry about that rouge wave coming up and soaking the unit and potentially frying it.
I just like using water proof units when hunting salt water beaches....the salt air, spray and sand always end up on the unit. The only non-waterproof unit that I use in the wet sand and suds is a CZ6a, but it's water resistant.
If I were hunting with the TDI, I would make sure to cover it up with some type of cover or plastic bag.
JC
