I have done full stalls in Commanders before. I had to do one a couple of years ago because we reskinned the horizontal stab, and it was a requirement.
What I have seen is that often a wing drops. If you respond promptly and correctly (i.e. lower the nose and use rudder to lift the wing), no problems. If you respond incorrectly (which, so far, I have never done or seen), I think that is where things could go wrong in a hurry.
Personally, for training purposes, I would recover at the stall horn, and you will be fine.
Where it can get really dicey is if the stall horn doesn't go off-- something I have seen more than once. There are a couple of reasons why the stall horn might not work. The big, obvious one is if the heat burned it up. On the Jetprops, and I think most 690s the stall warning heat is on the R PITOT switch. The AFM, for the 980 at least, says not to turn the R PITOT on until after takeoff.
Specifically, in the ice and rain section of the 980 AFM, it says :
"CAUTION
To prevent damage to the Stall Warn Heater on airplanes S/N 95000 thru 95040, do not operate R PITOT heat for longer than 10 to 15 seconds when the airplane is on the ground."
Secondly, if you look at where the stall vane is and where the fuel cap is, it's not hard to imagine an inattentive line service tech inadvertently dragging the fuel hose over it.
Now, combine a non-working stall warning with either a training situation or simply diverted attention with the power levers back in flight idle, throw in maybe a little bit of misrigging so the engines aren't perfectly in synch, and you could end up in a bad spot.
One really, really nice thing about the S-Tec 3100 is the underspeed protection that it offers. It is purely based off of indicated airspeed, and it gives you a verbal warning and, if the autopilot is engaged, will lower the nose on it's own.
