Half way through now. Enjoying it. Amusing that the main female character (from Tokyo) bursts out laughing at the male protagonist because of his accent - telling him he sounds like an actor in a period drama.
I lived in Ehime prefecture in Shikoku for a year and basically, you just get used to it.
Where I was, they speak a dialect called “Iyo ben” (Iyo being the old name for present day Ehime):
The first day teaching I had no idea what the kids meant when they asked me “ペット飼っておる?” but after a while I started expecting it.
I would say most Japanese who grew up with a more mainstream Tokyo dialect would understand most of what is said in regional dialects, at least the general gist.