We moved from MPH 5/6 to PHSE this spring and it went really well. Our library actually has several of the books so I let DD pick one to use to finish up science for the year, and I think it is a great fit for her.
Agreeing with everyone else that the HOTS book is great. I really wanted to like the entire program, but DD had already done so many of the experiments in outside classes that those were not very thrilling, and the textbooks and activity books are, as others have mentioned, a bit thin.