Jimmy is a strong, completely professional performer (in my somewhat limited exposure to him). There is no question of how "good" he is; the question is rather how much his style of music would appeal to you. It's a little hard to put a label on; he performs mostly, if not entirely, his own songs, and they blend "folk"/folk/trad./rock/Celtic/pop/C&W influences. Not much relation to Jools Holland and R&B, I shouldn't think. (I'm not familiar with those other names you mention).