Not yet - I've been following the progress of SYOS for several years now and I'm quite intrigued by their products - it's good to see them doing well. But I've not yet got enough money for a custom mouthpiece - plus I'm thinking long and hard about what the ultimate mouthpiece would be like.. I'm fairly happy with my 8* ebonite Lawton BB so something similar to that
I could probably get Morgan Fry to modify a Berg Larsen for less than SYOS charge for a custom piece, so there's always that option.
As one of my friends put it, the mouthpiece obsession is all about getting that extra 5% that you can't get out of your existing mpc.