I'm certainly wary of spinning, especially flat spins but I do like instructor trainees to get a taste for how aeroplanes can suddenly misbehave as distinct from the standard spin entry.
During the extensive spin tests done by Bill Kershner in the U.S., the aerobatic training community became aware of potential problems with the 150/152 Aerobat series when the aircraft was spun deliberately through PSG, incipient, and on into EXTENDED erect spin mode.
It was noted correctly that specific aircraft were prone to specific spin behavior due to rigging, and especially cg consideration even to pilot co-pilot weight factors and differing fuel load.
As with most aircraft, it is entirely possible to see differing spin axis development in the 150/152 series as the inertia and aerodynamic factors in play for a specific aircraft in a SPECIFIC spin entry come on line during the maneuver.
This is especially true if outspin aileron is applied to accelerate the spin and power then added (in a left erect spin in the case of a 150/152 due to needed gyroscopic forces) to flatten the accelerated spin mode.
I would strongly note in addition to what you have already correctly said that pilots doing long time line extended multiple turn spins in these aircraft be COMPLETELY aware that these multiple turn stabilized spins were NOT part of the certification process and that in every such spin attempted there is a fairly reasonable element of increased risk involved.
I note from one poster's film clip such a spin entered holding inspin aileron and no parachutes being worn. THIS is a situation I would highly discourage were I privy to this pilot's ear.
Dudley Henriques