I have the liftsaver on a Ranger Z21 with the Ulterra. Great mount and very solid. I find it's difficult to move it from within the boat but I think it's more the weight of the Ulterra than the mount. Interestingly, I have found that my Ulterra doesn't hit the trailer roller so I just move it forward while on the trailer before I launch. But my Ranger boat cover doesn't fit with it forward, so I shift it backwards when putting the cover on. The liftsaver guy is on TFF and is very available for questions or customer service issues. He helped me troubleshoot mine (turns out I didn't have the pin in all the way, dumb me).
In all fairness, I have not used the MK mount so I don't have a point of comparison. But I'm very happy with the liftsaver.