I've tried it on various conversions, compared to Handbrake and iFFmpeg.
- repacking of a .mkv in a .mp4 container with the so-called "Superspeed" setting: 18s (8s for iFFmpeg...)
- whenever there is actual conversion, it performs equal or slower than the two others
- the only point where Movavi beats flat its competitors is when trimming mp4 to mp4, there, the "Superspeed" thing is amazingly fast! (quite instantaneous where iFFmpeg took 45s!)
So if you only have to trim a lot of movies, with no conversion, cropping or else, go for it!