While I am hardly an expert on bump stocks, I am under the impression that they cause significantly more loss of control than normal full auto. They also will not cut off automatically after three rounds. Long story short they will mean fewer aimed shots, more stray shots, and waste of ammunition. All these will mean the weapon is less effective than the same weapon without a bump stock.
Bump stocks therefore appear to be little more than a toy to increase firing speed while neglecting everything else.