rampantlion,
I think there's at least a couple of different lines of "Conflix" buildings, but I think you're referring to the ones I use for Medieval purposes. I also have a Hudson & Allen Castle, and have used these Conflix buildings in siege games featuring that castle. The Conflix models are a bit larger scale, but not enough to prevent me from using them together. However, it may be easier for my mind's eye to blend the slightly smaller scale castle with slightly larger scale buildings, or vice-versa, as opposed to if it was just buildings side-by-side.
Here's some pics which I hope will be at least slightly helpful:
EDIT: I agree with Atheling -- who posted while I was taking those pics -- that Conflix are more cartoony/stylized. But same as re: the difference in scale, to me the difference in style is not extreme enough to prevent me from using them in the same game, at least from time to time!