It seems a bit of a blunderbuss device that can have consequences for innocent parties with a whole range of medical conditions, rubber bullets are bad enough, but they are normally aimed at legs and they even get that wrong as people have died. So at the moment I'm in the not sure camp until it can be proved safe and how are they going to prove that without using them?
A better solution would be an accurate water cannon with indelible ink in the water. Then the police later could go to the area when everything has calmed down and arrest everyone with the dye on them or their clothing and have to account to why they were in that location. Any innocent person would leave the area if they did not want to run the risk of being involved.