I've only paddled both boats at the Newfound Rendevous a couple of years back, but I would have to say that the differences are substantial. The Guillemot is a fun turn-on-a-dime play boat. The Night Heron is a faster straight line boat for covering distance. I think you could feel the difference inside of 5 minutes.

BTW-I am still building the Guillemot I started back then. The good news is that I am making progress on it and should launch it this summer.