It removes the physical sensations, and the "oh Sh!t I'm going to die" panic factor. The same recovery techniques can be taught in a real aircraft, that is fit for the purpose. They are few and far between however, and there is the basic problem. 90% of training aircraft are not suitable for unusual attitude and mishandling training, therefore it is not covered, or only covered in one or two lessons.
There are innumerable pilots and instructors that have never been beyond 60 degrees angle of bank, and then they are expected to perform a recovery, at night, in IMC after some simulator training.
I think it
is a bit unrealistic to expect airline pilots to do U/A training in a fit-for-purpose aircraft. However, I think it is definitely doable in the sim. Start off with wingovers, simple but getting harder cross-ref exercises, then go on to barrel rolls and if your sim will do it, loops. The critical issue is not the seat of the pants feeling (which you have to ignore anyway) but getting your brain to reliably interpret rapidly changing instruments.
Then move to closing your eyes, get put into a (at first gentle) UA then recover. Then ramp them up as proficiency increases. Some people don't like closing their eyes. IMO that's what has to happen to get any real value out of it. Somehow we have to train against the startle factor and sitting there, eyes wide open, while checkie Bloggs sets up a UA is just a waste of time.
The other point is that you have to do enough of it, and recurrently, to maintain the skill. Time for an extra day in the sim...