Why CGI? What is wrong with conventional make-up and prosthetics? Those can always be touched up in post-production.
Because it's not just his face, it's his whole body that would be partly covered in the tech. And combining real life with CGI still doesn't work when it's half and half.
Yes, conventional make-up WOULD work better. But for some reason CGI was used, probably to make the bits where his body transforms.
IMO, a better approach is just using a fully transformed/covered character.