We are Teaching Textbook lovers here. One reason- with MUS, I couldn’t even help my son when he was stuck. TT worked better for us. He loved the presentation of the lessons, and had no issue retaining the concept.
Like you, we had success with MUS until we hit Algebra and then it all fell apart. We watched the videos with him, worked the problems, but it was to no avail- we found the program to be oddly written and he struggled with understanding right from the start. We switched to TT, and he soared.
Just FYI-if it matters to you, MUS is now explicitly and purposefully aligned to Common Core. I did not know that until recently. Because I used the older versions, I can’t speak to how much the newer versions have changed to make this alignment. For some families, this makes no difference, and if it doesn’t concern you, then carry on. ;).