Having just been through the process of hunting down an MXT myself, I believe that the Original MXT Tracker series and the MXT 300 are the early versions, before MULTI-TONES, GROUND GRAB and BACKLIGHT. You can identify older models as they have a TARGET ID reference sticker below the LCD display for the 3 different hunting Modes; Coin/Jewelry, Relic, and Prospecting. The MXT Pro and the MXT All-Pro have 3 touch buttons in place of the target reference sticker. The 1st of the buttons has a picture of 2 - Musical Notes, the second is labeled Ground Grab and the third has a Picture of a lightbulb.
I have only a few hunts on my MXT All-Pro, but already have a preference for the Single Tone and am experimenting with the Relic Tone-2. I came from the Explorer / etrac world where there is A LOT going on in the headphones, but the ears and the brain eventually figure it out. At least I think so. As for my MXT, it is too early to tell what I will stick with, still learning things and figuring out what works best.
Best of luck finding what suits your fancy,
Rich -