I don't know about feeding Rabbits but for the commercial food's there is not that much difference except for a few add in's and take out's of plant's. Looked at a typical good feed Rabbits, i think.
http://www.dodsonandhorrellonline.co...9c8h7kgpdlt393
Some are edging on 17% protein and seem to mention digestive additives, this could be any plant that help's. Finding a break down on them and comparing with a tort pellet would help.