I'm another Zon player, currently owning two, and I'm not the least bit worried about not having a trussrod in it at all. If there is a neck issue, I'm confident that Joe would take care of any issue that would come up.
As far as Roscoe being a similar instrument to consider, I own a Roscoe, and it's very different in terms of sound and feel. IMO, the Roscoe has a bigger sound than the Zon's. The Zon's also tend to be on the brighter side to me as well.
I haven't played a Kinal, but I do know others that have, and they swear by them. I'm sure if you went that route, you wouldn't be disappointed at all.