Owen Lowe notes:

What do you imagine could happen that would make this method so unsafe?
The insert is secure left to right by the throat opening. It's
registered and resting on the rear lugs - all downward motion (as I
mentioned, about 3/4") of the insert is stopped once it hits the forward
lugs and by then it's fully secured by the front of the throat opening.

It's really no different than a plunge cut on a table saw or a
table-mounted router.

Yeah, it is. The piece is too small to grip safely.

Charlie Self
"When we are planning for posterity, we ought to remember that virtue is not
hereditary." Thomas Paine