Not sure but i think they are made by cosworth, and yes they are generally better (i have run greddy pistons in about 7 engines (SR's and RB's) now) than the run of the mill probe, mahle, CP, JE etc but the reason they are generally better is they come out of the box with killer ring sets better crown profiles and base stock but as for life there is not much in it if it is built properly.... we get the same life out of JE's (our most used brand)... wear on the thrust side and audible slap @ 10,000km was a builder issue not a piston issue.
The greddy pistons (again i think cosworth due to very odd ring sizes) are generally quieter and run finer tolerances as the base stock is better but @ up to triple the price you could do another engine for what you saved... I use them only on high end builds and my own stuff.