I use SimpleMovieX for cutting/editing MP4 files and from my point of view, it is doing the job very well. With mp4box you only can cut at I frames and it is a command line tool. Quicktime saves only mov, but not mp4, or re-encodes.
With SimpleMovieX you have frame accurate editing for mp4, and lossless save. I havent found an mp4 editor on MacOS that is doing this and is affordable.
I agree the UI is sometimes not obvious to work with, but if you understand the logic, it is ok.
I tried larger movies >2h, and cut away some commercials, no problem, or trimmed some music videos, w/o issues.
So I havent fully understood, why some ratings are so low. There is simply no alternative, or someone should point me there...