"-MIKE-" wrote

It's only to clean up the hole, after having drilled down all the way in
several places.
I've seen guys demonstrate it and they all had their own technique that
worked equally well.
I do wonder how it might be retrofitted with a trim router and good
router bit.

There are all kinds of router mortise jigs out there. The difference with
this product is that it is much cheaper. There are a whole spectrum of
mortise options available. From cheap to exorbitant and everything between.
You pays your money and takes your choices.