Well, locking wheels is not desirable in any case, FWD or RWD. When you're braking as hard as possible, any judder or shake can disrupt the balance of the car, that's why heel&toe downshifts are always the best.
I always downshift with heel&toe while driving in my car. It makes the shift feel much smoother which is also nice when you have a passenger next to you (plus you can impress them with your monster heel&toe skills
).
What I've noticed is that definately not all cars are as easy to H&T downshift. You need good pedal placement and preferably an engine that responds to throttle blips as instantly as possible, with the least amount of lag.
I started doing it some 5 years ago and it took me a while to learn, but now I can say that I'm fairly good at it and do it all the time. I even use double declutching together with H&T sometimes, especially when going down to 1st gear. It's fun to do and very rewarding if you nail a couple of H&T downshifts just right
