I can't recall reading anything on their site about cast one way or another, I don't detect any on mine. The fit and finish is quite nice, much better than one would expect in this price range. The DeHaan imported Huglu's to me look even better than the CZ imports.
Are they stiff? Maybe a wee bit but not anymore so than other new guns. They are well finished and the stiffness you'll detect isn't much and isn't a result of poor finish on fitting parts like on say the Stoeger imports. Yes they are well balanced. The guns I've bought are .410 and 28 gauge guns. I don't shoot the 12 any longer due to my shoulder.