I bought a few sets way back when I was testing the waters of keyboard customizing.
Decent quality, could be thicker, but can say that pretty much about any keycap.
They felt crisp typing on, but my biggest issue was something I've never really experienced with other caps is that the spacebar became extremely painful to use. In hindsight I guess I could have rotated the spacebar 180 degrees, but I don't like the way that looks.
Long story short - They are worth their price - but probably not much more, sore thumbs!