I have the Goodwin. It seems to work as advertised, is cheap, and installed easy. Certainly makes it easier and more accurate to get deflection perfect than the OE Yamaha shims. And I'll add that it reduces rotating mass by a very insignificant amount. I only mention the weight because a few people on HCS feared it because it "looked heavy" and they didn't want to add mass to their clutch. So I personally weighed everything, found it to be almost an ounce lighter than the stock hardware it replaces.
But I haven't actually ridden with it yet, and I don't know anything at all about the Mountain Perf or other brands to be able to offer you a subjective comparison as to which is better.