I haven't handled or shot the 6", but I've shot the blued 4" if you don't mind my input anyway. The weight wasn't excessive. Chiappa lists the weight of the 6" at 936grams, which is about 33 ounces. A S&W 686 with 6" barrel weighs almost 45 ounces.
With 158gr 357 factory loads recoil were definitely more pleasant than out of my 4" Colt Trooper (which is probably heavier than the 6" Rhino).
The hammer/cocking system is strange (the little red "COCKED" indicator that pops up), and seems like it could possibly fail prematurely. Just an uneducated guess, but it seems overly complicated compared to a normal revolver's hammer.
Another possible issue is that the placement of the barrel pushes very hot gases out of the cylinder much closer to your support hand than on a normal revolver. Just be careful about how you grip it, I was aware of this before I fired it and didn't feel anything unusual.
Minor gripes aside, the only real flaw I found was the grips, which should be identical on both 4 and 6" models. They're too squarish (they bite into your palm with the square edges), and come to a point at the butt which was uncomfortable for me. I feel like the Rhino would benefit immensely from a more ergonomic grip, or at least the stock rubber grip, but I think those only come in smaller sizes intended for the 2" model. I would consider buying a Rhino if I could find some better aftermarket grips. Because the Rhino is such an unusual specimen, I'm afraid aftermarket accessories (as well as those licensed from Chiappa) are few and far between.