I've tried Rubi cutters, but I didn't really like them. I used Sigmas until fairly recently, when I switched to Montolit, which in my opinion are among the best cutters you can get.
Without really trying, I can cut slivers just a little over 1cm wide, out of 10mm thick 33x33cm (larger than that is rare over here) Porcellanato, which is the densest, hardest grade of porcelain.