I'd never heard of Ultex; a bit of Googling revealed that they are 'a new, premium brand for tradesmen'.
On the basis that they're a new brand, I doubt anybody will know what the longevity of their sharpening stones is like yet. On the basis that they are aiming at the 'premium' end of the market, probably should be OK. Well - you'll find out for yourself, in time!
One small comment - looking at their website, the finest diamond stone I could see was 1200 grit. That should give a perfectly adequate edge for most duties, but for the ultimate polished edge (end-grain paring, final finishing smoothing plane irons and the like) you may find you need to invest in a finer stone eventually. I gather that there's an 8000grit diamond stone about (not sure who makes it), but any 'polishing' stone should do; translucent Arkansas, Welsh slate, high-number water stone - even fine diamond paste on a piece of flat metal.