The problem is, it takes a lot more justification to fire a bullet than it does to use one of these.
One of these and 2 or 3 people can effectively fight a crowd of thousands. In fact there is no reason for any government NOT to use these to quell their population and keep them goose stepping in line... except for morals.
Furthermore, if a group or government is willing to use a cheap bullet in a situation they would be highly unlikely to purchase, train crews, and deploy these expensive non-lethal weapons.
While these weapons definitely have their uses, they can also easily be abused. Perhaps even more easily than lethal weapons, since there is supposedly no lasting damage done. (Unlike rubber or plastic bullets which cause moderate too severe damage, can be deadly and are inaccurate.) I expect China to get a lot of use out of their purchase from now on.
And on a final note, a lot of these weapons CAN be adjust to cause permanent damage. A lot of the R&D for these weapons was to design a targeting system to keep them from doing that. Change some settings and depending on the weapon large portions of a targeted crowd may never hear again or may never see again.
