Yes, Crispr-cas is actually a much more novel type of gene targeting. It is very interesting and it too has its side effects and draw backs. I think it is much more plausible that Crispr will be used sooner than megaendonucleases. They are much easier to manipulate and alter. It is really a great subject of research! HUGE opportunity for major scientific advancement in gene therapy field, it is tantalizing!