We have used LOF Fractions, and we are now finishing LOF Decimals and Percents. We don’t do any other math programs, but we use the flashmaster (and electronic flashcard system) every school day. I also found that my son (finishing 6th grade soon) wasn’t retaining the information in the LOF books as much as I would like, so I put a few problems (no more than 5) on the white board each day for extra practice.
We like the books. My son enjoys the story about Fred. We will continue with the series, but I think I will supplement LOF with MEP this coming fall. I use MEP with my daughter (finishing 3rd grade soon) and I REALLY like this program. When she is old enough for LOF, I will use the two programs together for her.
From what I understand, the series becomes more challenging once you are in beginning algebra. Then the books have a companion book for extra practice. And the series is supposed to be a very thorough stand alone math program.
Sarah
After rereading your post, I realized I didn’t really answer your question. 
We don’t use MUS, but I don’t think it would be too much to do both. The books aren’t very long, and each section isn’t very long.
I do think LOF will be enough to prepare for college level math. But your child might need to supplement with the first books that don’t have the companion books with the extra problems.