I only got to use a Sigma when I arrived in Australia and got a contract with another tiler. I couldnt help notice the absence of Rubi. I asked what they used and it was Sigma all the way or a Clinker ( arf arf) . On entering Beaumonts tiles ( major player in Melbourne) I went for the Sigma . That was August 2001, I still have the same cutter and its used most days.
Every year I take it to pieces and clean the mess off it, Oil it and assemble it. If I am feeling generous then it gets a new wheel whether it needs it or not.
When I came back to the UK and entered the Tilers Forums I was scoffed at but who is laughing now and who was right all along.
Sigma have made huge marketing steps in the last couple of years but if you are happy with which ever cutter you use then thats all that matters.