I’ve met both, albeit Nicholls only briefly, and whilst Henderson is the more personable and approachable, I’m inclined to believe that there’s a certain amount of front to it. I have seen him in a rather less amenable frame of mind and it wasn’t particularly pleasant. With Nicholls I think that what you see is what you get.
I’ve visited both yards several times on non-public occasions and prefer the Ditcheat operation. There seem to be few horses with vices, which is usually an indicator that they are relatively happy and have plenty to keep them interested.