I have the Hatsan version of the same compressor. Gotta love them, they replaced the first one I got. Then they quit supporting them all together. I ordered a bunch of parts from Ali Express. 2 rebuilds in 4 years. It just crapped out again. Not sure if I will rebuild it again or just junk it.
I added a ST Compact TRS. I also 3D printed some spacer rings for the barrel, still using stock shround. 25 Cal MKII dead on with no POI shift. I hunt varmints in TX so the gun gets moved and bumped around a lot.