The MRX turbo is the "ST line" of the Fiesta ST turbo world.
It's not like Mountune would have done a hybrid and, at the time the MRX was being finished up, Garrett pulled the rug out by releasing the GTX Gen 2 series. I just finished reading most of the thread about the MRX and, in 2017, people were really happy with it. Now, it's kinda awkwardly positioned as a more expensive, slower spooling, similar power option to Ron's hybrid and maybe the X-47 (non-R) or a similarly priced, similarly spooling, lower power option to the GTX2860R Gen 2. I understand the reasons for a hybrid and for the GTX2860; I don't understand why someone would go w/ an MRX. If you're concerned with the reliability of a hybrid or want big power, go w/ a GTX2860R Gen 2. If you're looking for a kick in the ass without having to buy aux. fuel, go with the hybrid.
With the S280 and X-57 flavors coming on board my guess is that the last MRXs are being sold right now.
With all that said, I would have leaned toward a used MRX over the X-47R that I bought (for a great price) as a first turbo upgrade if I could have found one. But, with either, I always knew that I was going to end up on a new S280, X-57 of some sort, or GTX2860R Gen 2 for the long haul. No way would I have spend GTX money on an MRX.