Phew! I'm glad FD stepped in there as I'm hopeless at explaining aerodynamics
Mark
I didn't really phrase that bit you quoted very well for the reason stated above. I meant that by keeping the same attitude you are giving yourself plenty of margin over the raised attitude slip not over the in-balence flight you are transitioning from. However, it will not be as efficient as a slip held at the correct attitude (which is slightly raised) . In practice it simply means that if you don't raise the nose slightly you will find your speed is same or slightly higher than it was when you straighten up but you will have travelled further for the height you've lost. In a well excecuted slip you will have to lower the nose slightly as you straighten up but you will have lost a lot more height for a given distance. Don't forget that you are not actually flying that close to the stall in the first place, you are at approach speed which is approx 1.3X stall so you have that margin too. If you get much slower it will be difficult to maintain the slip anyway, so the are plenty of clues apart from your ability to fly by attitude. I use the term attitude over AoA simply because I'm looking at it more from a pilotage point of view. AoA is very difficult to think about scientifically as you fly, whereas your training should have shown you that your airspeed is fairly easy to maintain by visual referance to either the horizon or aiming point and is safe enough under normal circumstances.
SC
Surely if you are at the point of stall you would expect an aircraft to possibly do odd things? It doesn't take much of an over imput of anything to diverge from S and L flight. It's a bit misleading to compare this to a properly flown intentional slip. I can see that as an instructor you might want to play it safe with what you say on here but I just think that you are over stating the danger bit. Sure, to begin with you'd want to practice at height, but once you are proficient and used to the slip characteristics of the aircraft you are flying it is essentially a very safe and controlled manouver.
SS