@cathal both zinc fingers and talen weren't common lab techniques, as far as I heard you would have always required a third party to produce them for you. In this case it's maybe easier to frame the for patent infringement.
Looks to me cas9 has more to share with polymerases. Yes, you can buy them (and how many isoforms are out there that have been isolated) but you may also diy. With the plus you don't have to isolate cas9 as pure protein and nobody prevents you from getting the DNA synthesised. Anyway I don't know if you heard but there's a new crispr system, Cpf1, discovered lately. https://en.m.wikipedia.org/wiki/CRISPR/Cpf1 Cheers, Fede
