Hi Jason.
I think that the AT Pro is simply a stand alone detector within the Garrett line up. The combination of features that it has, although all of them exist in other detectors, they have all been rolled into one.
You'll find that the GTP although only has 3 sizes, is an advancement in the imaging concept, compared to the GTI's. The GTI's need the imaging coil to work, but the GTP doesn't. The GTP has only been around for 2 or 3 years. I'm sure that Garrett will improve on these machines in time, but as you can see, these 2 detectors will have absorbed a lot of their R&D funds. You'd be amazed at how much time, effort and money it takes to develop something to the point you can manufacture it. Coming up with the idea takes only hours, yet developing, refining and overcoming all the associated problems, takes an enormous amount of persistence, time and money. I imagine that we could expect a new high end machine in a couple of years at the earliest, given the effort that has gone into these new machines.
I hope that this doesn't discourage you. Personally, I think the the imaging feature on the GTI, is one of the best visual indicators of sorting coins from other targets, that I've come across. ( I was luke warm on it for a long time, till I figured out how to use it to good effect.) It will be interesting to see how Garrett improve on it in time.
Mick Evans.