This was the very first keycap set I ever got, more than a year ago. It allowed me to experience the greatness of GMK keycaps first-hand. They are thick ABS (1.5mm) with pretty much perfect legends. Their thickness gives them a nice bassy sound, which I enjoy.
ABS gets shiny over time, but the shine is less evident on light-coloured sets such as "True Olivetti". If you hate the looks of shiny keycaps, I recommend you going for a light color.
The price is high, but I think that, all in all, these caps are worth it. It's not my only GMK sets. I've since acquired many more, and expect that trend to continue. Cherry profile is a pleasure to type on!