I tend to side with the police the majority of the time in these situations. If they thought the suspect was able to use deadly force (knife) then it made no sense for them to use non-deadly force (taser, baton). Doesn't seem like anything illegal happened, based on that video.
A couple things generally about these kind of events...most people on this board, myself included, have no idea how they would react in a situation like this. If you say you do, you're lying or deluding yourself. Unless you've dealt with violent people or the mentally ill regularly, your opinions are moot.
NPR did a recent story about autistic persons and the police. They are MUCH more likely to be confronted by police and arrested than your average person. They simply don't act normally, which is suspicious, and they don't know how to effectively communicate with the police. It was an interesting piece and something I had never really thought about. With our society's push toward inclusion, these interactions are only going to become more common.
Certainly our police are inadequately trained to deal with this, but that training is going to be expensive and possibly not all that effective.