I'm not a professional beat-boxer, but from my layman's perspective, Blake is very good.
What I like most is his ability to mix it into his songs so flawlessly. I watched the videos of the original artists (who are all phenomenal), and Blake did not copy cat them - contrary to what Simon said. Blake really does have his own style which he brings to these songs.
I love this kid. He'll have a job in music the rest of his life - either as a performer or a producer or mixer.