Mike; while I've not yet purchased his unsharp mask kit, I can attest to the quality of his production methods. I've met Alistair a number of times, and had extensive discussions about his products. He's passionate and knowledgable about what he does. His product quality is very high, as are his machining skills/tolerances. BTW, he also makes a great dye/dodge mask kit too.
He's also supplied his masking kit to a number of very well known shooters in the States.