I have used all the Explorer models up to and including the SE. I currently have an SE for a backup to my CTX3030. The Explorer models all do an outstanding job. These detectors have the same basic platform with changes here and there but all are great. My son uses an Explores XS and will not let it go for anything. When it comes to deep iron all detectors I have used over these 40+ years have some problems with deep iron or iron that has rusted almost back to dust. This problem is one that I can live with as it tells me I am not missing those old deep coins. The soil matrix and angle of the target in the soil matrix, wet or dry soil, salts, how deep the target is, sweep speed of coil over the target, and other matrix factors will cause these kinds of irritants you speak of. There is a point when the response of iron at dept has a particular sound and response when sweeping the coil from different angles over the target that will help to dig less of them. It is by digging some of them that you become aware of the differences that give you the confidence to pass over many of them.
The FeCo numbers are a"best guess" by the detector. When using my SE I hunt in digital with expanded on and switch to iron mask for additional clues. You will notice that most detecors with an LCD screen only show the Co (Conductive) number or dark spot under a name or icon for a target. The ones that have iron discrimination is based on the magnetic properties of iron. This is still a best guess depending on the factors I have already mentioned above.
Good hunting,
Cody