just want to mention I have owned this pin nailer for awhile now and have to say as much as it is more money it is worth it's weight between having a lock out feature to having power to sink 2" pins into the hardest of hard woods is just crazy...
Don't have a Grex, but my pin nailer gets used very often. Being able to position something then pin it there without leaving any significant mark is terrific. The one I have is limited to 1 1/4 inch, but it is a fraction of the cost of the Grex.
23 gauge is pretty fine, .02" or .05mm, Mine is 18 gauge which is .048 or 1.2mm X 2'' long, I am surprised they can be driven with out bending over. Way back when we used to use the Senco staplers with 12 ga./2.5mm to install plywood sheathing on houses and they were 2" long.