I thought this was interesting, given the recent posts regarding this...[www.youtube.com]

Interesting.

The only thing is, with the way he does it, you will have to drill through the original flange below to the subfloor to secure the new top flange. There is a chance the subfloor right under the old flange may not be solid especially if it's original cast iron and they might have put a thick cardboard around the piping when they poured the concrete leaving a sleeve around.

The new flange also reduces the outlet diameter.

Those are all good points sum. Most of the homes in your neck of the woods are built on slabs. Around here, the flanges are screwed into plywood. In most cases there is no attempt to add blocking. Wet plywood doesn't hold screws for very long. But then, nothing is built to last a lifetime any more. It's a disposable society.

if the original flange is in good shape and secured to the floor then no need for additional screws to hold the sandwich together.
think about this...
the toilet bowl is pressed down into the wax seal and secured with bolts and nuts in two places.
if you smear bowl wax between the flange and the extension and then secure that with an additional washer and nut, what makes the difference ??
yeah, of course, if you can add a couple of stainless screws it does add some strength but to me it is like wearing a belt AND suspenders.
the seal is only going to be a good as the weakest part. that being the area where the wax meets the porcelain..

Just makes me happy to see that some people actually care about a proper flange installation.

My estimate is that 2 out of 10 flanges I see are properly set to code.

Packy everytime I saw you call that stack of flange/spacer/wax a "sandwich" I laughed out loud.

i call it a sandwich...
some call it a "spuckie"
look it up.. you gotta be from boston to cabeesh or terms..