Yes, the MXT 300 is just an original MXT that came with the 12" concentric coil and the newer flat black paint for the control box. It is every bit as good as every MXT performance-wise.
I have both an original MXT and an MXT All-Pro. All models of the MXT have identical performance! The only differences are that the Pro models have a couple of extra features like 7 tones and ground grab, but the basic performance is identical. Frankly, I don't miss the Oro features when I use my original MXT. I hunt in 2-tone relic and don't use the 7-tones, and hunt in locked ground balance with an occasional flip of the toggle to update the ground balance, or leave it in auto, so I don't miss the features of the Pro. I have a Pro and like it, but I end up just using it like a regular MXT.
The MXT is one of the all time great detectors ever and can easily hang with current top of the line models. White's almost made the MXT *TOO* good because there's almost no reason to ever have to upgrade. I've owned a CTX 3030 and a V3i, and the MXT has just as good depth, target ID, and separation as either of them,at least in my mild soil.