Well CRISPR works in flies as some of the fly stocks have been switched from using RNAi to CRISPR for their gene edits.

Fly immune systems obviously are quite different. But the technique still holds a lot of promise. Like any cutting edge technology there are potential problems in developing it into useful therapies, and there is a chance something better will come along and displace it.

It is very difficult to edit all the dna of living organism as each cell has a copy. Easier to do as an organism develops.