Not true.
The don't apply brakes (so can go above the sopeed set on a downhill), and you can override them by pressing hard on the accelerator. But if you use the accelerator normally, and are not on a downhill, they will prevent you accelerating above the set speed.
Most cars have had manually set speed limiters for some time now, including both mine and my wife's 2015 cars. Mine is too easy to override, you don't need to press the accelerator as hard as you should. My wife's is better that way.
The difference with the ones required since July is that they set the limit (to the speed limit of the road), rather than you, using GPS or signs or a combination to decide what the limit is.