We have been looking at KK 50 open and 58 recently in order to think about buying one.
Visited hull #1 of KK 50 Open, few days back thanks to owners Larry and Janet. They were very helpful and graciously answered all our questions about that design.
We also looked at KK 58 at a recent boat show. 58 is more traditional design. The biggest difference, I found was about living quarters - more light in saloon, because pilot house being on same level as Saloon in 50 open. Build quality appears similar for both. 58 being bigger in size feels roomier. Engine room has lots of headroom. Have no experience of motoring either as we are new to powerboats.
50 open is new and has fewer boats built so far as compared 58. We liked 50 open slightly more.
HRK