Spock Must Die is a good read, but I don't see how or why it would be appealing to non-Trek fans.
It's by James Blish, a very important and well-regarded science fiction author. There are lots of Blish fans who aren't Trek fans.
Planet of Judgment wasn't all that great, mostly because I found the aliens annoying.
I think it's the second-best of the Bantams, trailing The Galactic Whirlpool