I've used them for years, either in the pool or if rarely in the tropics without a hood on. Water can go in your ears anytime. The worst time for me is if I turn too much while donning fins in 4' of water, also if I flip around too fast while diving. The hood and plugs don't go well together (for me, the hood messes up the plugs stayng in and I gain nothing since the hood does the same job). I think each does the same generally good job keeping water from going very FAR into the ears. I still about 50% of the time need eardrops after diving. I feel there is no difference in the ability to equalise. Some say the plugs actually make it easier, but I can't follow the science in that, since it would seem easiest with your ears completely open. I've never had equalising problems, so I'm not the best judge on that.
You're equalising all the time. The closer to the surface the greater the pressure change, so the more frequently you have to equalize going down. Coming up it happens naturally unless you have congestion of one kind or another. I don't know what is meant by water not going in the ears until below 20'. Water gets in swimmers' ears at the surface, thus "swimmer's ear' (otitis externa--I just like saying that). Plugs falling out during a dive should make no difference except you'd (I'd, anyway) be more likely to get water in deep and need eardrops.