I've had a saw like that for 35 years, different brand. It is a flush cut saw as the teeth are set so they don't scratch the bottom contact place.

I used it to flush cut wooden plugs for screws for furniture. I have also used it to cut off expanding foam used to fill gaps.

However, we never use it to trim door jams. Using it the way the video shows leaves a kerf width of a gap... and - the cut is rough. No - wrong tool for the job. Get a Japanese pull saw - very flexible, very sharp, thin kerf.