Firstly, i have no experience with J-Nats.
Secondly i use slurry as part of a progression from the same stone (Escher) slurry to water only. Same razor gets refreshed on the same stone with water only. At that point if you use slurry my guess would be that you run into "Slurry-Dulling" when your actually just wasting a precious stone. The key is the knowledge as to when the razor needs refreshing.