If it has the original 300mm, 12" coil it is not suited well for beach hunting. The 300mm coil does not handle high mineralization very well. If you use a smaller coil or Elliptical coil, it would make a good beach hunting detector.
As far as the detector goes, there are only two versions of the MXT which are MXT & MXT Pro. The MXT was sold with several coil options and the detector was labelled differently for each coil setup. For example, the mxt 300 & mxt e-series are completely the same except they are painted and labelled differently since they came with different coils. I think it would have simplified things to make every MXT look the same regardless of the coil it was sold with. After a few months/years its a successful marketing strategy to change something minor and relabel it and make more sales because people want the latest product. Most people that are in the metal detecting hobby have more than one coil. If you own an MXT 300 you probably have other coils for it. Once you change the coil, its still labelled MXT 300 but the label becomes ignorant or non-relative at that point. It only means it was sold with the 300mm coil.
The MXT 300 can be setup with many other coils and would be good for beach hunting.