The purpose of the D3O isnt to be the best protection. It is supposed to be the best protection that doesnt hamper your freedom of movement. For that purpose it works pretty well
Exactly. If you don't like wearing helmets, they have beanies with d3o in them. It offers some protection, and some freedom. I personally prefer a helmet though.
Long term, after more testing future iterations of the product it might eventually compete though.