Wondered what professionals think of this technique? Looks like it is fine, but did not know if there are any safety or other problems that need to be watched.
Seems like a good trick to me. I've never tried to cut a saw zall blade with a pair of tin snips before but he sure made it look easy. As far as safety goes, I'd say that's a hell of a lot safer than a full blade cutting blind into a wall.
For a job that size I would just use a sharp keyhole saw.
If it were a bigger area I would take a short sawzall blade and put it into the sawzall backwards. This allows you to keep the blade a lot closer to parallel with the wall because the handle of the sawzall isn't getting in the way.
With a little practice and concentrating on keeping the blade as close to parallel with the wall as possible it is pretty easy to guage how deep you are cutting into the drywall. You can also cut right along the middle of a stud like the guy in the video did.
I will keep this in mind though as a use for bent sawzall blades that I would normally just throw away.