Minus the o-rings that come with the kit, provided it is properly lubricated with good o-rings, you can get a perfect seal. The parts are milled great, have a nice heft to them, the trigger pull is nice and smooth, the catch has a nice defining click, the rambase is indestructible. When fired, the heft of the plunger actually gives the caliburn noticeable tactile recoil, which is an awesome effect. Make sure it is properly lubricated, though, or you will lose FPS. Overall an amazing value for the money, I just wish it came with an extra silicone shock pad.
I can confirm these fit into my Gobb-Snogga made by captain slug himself. Had to finnegel some pieces a bit the sear ended up being a bit loose on the sleave that goes around the pivot screw. I used a piece of e tape as a shim to tighten it. The plunger head works great and fits K25/26 just fine.