I had GK1 (.25 cal) and now own the standard Mordax. I don't know why but I have mixed feelings about the GK1. I still believe that it is the semi-auto pistol which all others are judged against, and I feel that it makes more power than the (standard) Mordax. Heck, my .25 GK1 (purchased pre-owned, and the first owner had it tuned by Derrick Wall) was slinging 33.95's at 827 fps/25.39's in the 880's. That's some darned power from a pistol length barrel!
My GK1 shot well and never gave me any trouble... but I still like the Mordax better. I had bought the adapter and used a stock with the GK1, so it was apples-to-apples shooting as compared to the Mordax. Pretty much because I don't find myself shooting PCP pistols very much (really only shoot my Manul as a pistol), but I like playing with mini-carbine form factor guns. Both the GK1 and the standard Mordax could be quieted down well with the correct thing on the end of the muzzle. Both were accurate, although I felt with the reciprocating parts the GK1 was a bit more prone to muzzle flip (but not to the extent I have felt with the .25 cal Huben K1 rifle). The standard Mordax just feels really solid when shooting. And on my 25 yard backyard range shooting rested guns, in my hands the standard Mordax is just a little easier to shoot more accurately as compared to the GK1.
Perhaps it was the power difference between the 2 guns? I'm not very power hungry when it comes to air guns, and prefer shooting something which is smooth and quiet over something which is powerful and brash. I just don't need the latter for my main uses (plinking and some very light pesting normally within 70 yards). And while the only thing which ever broke on any of my multiple Huben guns was the pot-metal magazine release lever on a K1, for some reason I was always concerned about Huben failure. Not that it should have been even an afterthought as if I couldn't fix something, resources like Kelly at Kraz-Cool was always available. But in my mind I am just more comfortable in working with the service dept. at AoA based on my past interactions with them. So I'm not as overall concerned about if or when my Mordax might have an issue (and none of my Mordaxi, nor my Sidewinders ever have).
I do have large hands (wear size XXL gloves), but the GK1 grip still felt big to me. The Mordax grip is more comfortable. And given the option, I do prefer the removable mag of the Mordax over the fixed mag of the GK1.
