Hi El,
I am not sure how to answer your question as to whether the GS 5 or the TDI is a discriminating detector. Both of these detectors are PI's that have certain characteristics built in that allow for a level of discrimination of objects, depending upon how they are used. So, yes, they have a level of discrimination capability.
They are not discriminating detectors like those found in the VLF series. Instead, the TDI and the GS 5 both have features that allow a level of discrimination, depending upon just how they are adjusted. As an example, lets say you want to hunt for copper and silver coins. You can adjust the ground balance such that most iron or ferrous objects generate a high tone while copper, silver and other higher conductor objects create a low tone. Using this technique and selecting low tone only (high conductor) will allow an operator to ignore most ferrous objects while still detecting copper and silver items. This feature works quite well.
A person can't simply look at a meter, or adjust any control to easily ignore any particular object like you can on a VLF, but there is a level of rejection that can be done. Normally, when searching for copper and silver coins, you will dig a certain number of screwcaps and some other junk that is considered a high conductive object, but normally, you will dig very little other trash such as nails, foil, etc. Large iron objects will give an overload signal, but are easily recognized with practice.
I, personally, have used this high conductor mode in parks and had great success finding coins while digging little junk. Fortunately, where I hunt the ground is bad so VLF's do not get the greatest depth. Thus, I find a lot of the deeper coins using either the TDI or the GS 5 at these sites. I suspect if the ground was very mild, I wouldn't be as successful, but do not know for sure.
So, to best describe the discrimination feature, it works but not like anything you have used before. It is also works best when hunting for high conductive objects such as silver and copper coins. The discrimination feature does not work as well when trying to separate out low conductors such as gold or gold rings from other objects. When in the low conductor mode, it is much more difficult to separate out the iron trash. In some case, it is almost impossible.
The best way to know for sure just how this detector works is to try to find someone who has one and is familiar with the controls and have them show you what it can do and not do.
I suspect that experienced PI users will like the added features, but experience VLF users will be confused initially and may be disappointed if they are expecting a sophisticated level of discrimination. There is no sophisticated level of discrimination like that found on many VLF's. However, there is a lot more discrimination ability on the TDI or the GS 5 than found on most PI's.
Reg