I just put a Mantis on it last night after writing my post but haven't played a game yet. It looks kind of odd, but then again, I don't think I installed it 100% right since you have to put two holes in the wood under the playfield... and I don't think I got it completely snug to the front lip of the scoop. The metal on the Mantis looks to actually be thicker than the Cliffy metal, making it an even smaller hole... however, the Mantis allows for the ball to still drop in since it leaves the small ledge like the original scoop.
It would be sweet if the Cliffy could replicate the small ledge.
I have had my machine since early October and have probably put a few hundred games on it... the scoop is finally showing some wear with ball indentations on either side. Doesn't look bad (yet) and to be honest, you don't even really notice it from a playing position. If the light catches it, you may notice it.