For those who don't know, Hypnosis Mic is based on a musical anime project where the voice actors sing and attend concerts based on their characters. Some of the songs are quite good so if you're interested to read this you should definitely go check their musical projects and drama tracks.
The idea, however, of making a manga about rap battling was not very good.
The universe and the story HypMic is set fits very well the simple concept of music projects, but not enough to build a visual comic. It became dull and childish to a bad shounen level.
I think this manga will only (and
maybe) be pleasant for the ones who are already fan of their musicals and/or songs, if you're new to this or an outsider, I hardly believe you're gonna enjoy such randomness, but nonethless, check out their musics and give the manga a try.