Well, in.my mind the downside to all is that stick-on velcro loosens in the hot sun or anytime the receiver gets hot.
Having that steel or aluminum plate insulates the glue from the heat of the receiver.
But it won't do anything about the glue that softens because you left your gun in a hot car.
All that being said I don't use a side saddle or leave my shotgun in a car. I do have some experience with velcro but maybe they're using a new epoxy or urethane to attach it to the metal.
Both of those will soften up under heat a little as well, but they don't come apart.