Just picked up these in preparation of the Analogue Mega SG which should arrive any day now. Haven't tried them on original hardware yet, but I really only got them for the Mega SG which I plan on keeping upstairs in the living room anyway (not downstairs in the game room).
First impressions are that the shape feels natural in my hands, and the dpad feels awesome, and has a nice texture. The buttons are the right size, and placed well, but click a bit differently than an original 6 button and feel kind of cheap. And the entire controller itself feels very light, a bit too light for my taste really. But if they perform as well as everyone says, that's all that really matters to me. And it'll be convenient using wireless pads in the living room.
http://i.imgur.com/F5igGSl.jpg