Rainbow uses a 15/64" high helix drill bit for their injections, ArborJet uses 3/8"... the high helix allows for a clean cut and better uptake. I have done injections with all of the systems and no one is perfect, they all can leak if not done properly or you have a decayed area in the tree. Plugs are not required to get to get uptake or for compartmentalization on the wound... we dont use plugs or tree paint on pruning cuts... why use them for injection? What ArborJet doesn't tell you in they have a plugless system that uses a small drill bit, APHIS requires it for all of their ALB injections, ask the local AJ rep.Also, the Rainbow system still requires pre-drilling but uses a slightly smaller hole.
The moral of the story here is that you should do your research, request a demo from each company, ask about the pros & cons and choose an injection system that best suits you and provides the best results (for the tree). With that said, I always consider different treatment options before I decide on injection because the facts are, you ARE wounding a tree - is there a better option?