The hulls they produce are indeed the old Metcalf Mouldings hulls, I've never seen one made by Models by Design, so I can't say how good they are...
The Berry Castle would make a nice model, but it would have to be built with a careful eye on the weight, especially the top hamper, as it's a very shallow and narrow hull, so would easily become unstable....
Having said that, with your experience with warships, narrow beams and stability issues are probably well known to you!

Regards
Eddy