I too remember being trained doing this maneuver in France. It was
called "retour au sol" (back to ground)
You could always tell when someone was closed to solo, as this was
part of the curriculum back then.

You would open the speedbrakes full, drop down below the tow plane
wake turbulence, and wait for the tow pilot do its thing. I do not
remember being told that we could stall the glider on landing. Perhaps
it was because you would need to close the speed brakes while flaring.
You obviously don't need them full on very short final.

Interestingly, I also learned this maneuver later on as a tow pilot
itself. And let me tell you that this is where it is actually the most
challenging! We had to remember that there was a glider below you,
underneath that wake. So you would have to arrive much higher on
final, even higher than when you are just returning with the rope
only. Landing was uneventful, you would just have to remember to keep
taxiing a bit long, to give enough room for the glider behind you to
stop.

It's not an necessarily an unsafe maneuver and I was surprised while
flying in the US that a tow release failure is barely mentioned.

Richard
Phoenix,AZ