Opinions are like... well, you know, everyone has one.
So I'll share mine in the hope that it might help.
I've had a .22 cal Hydra for almost a year. It is not a gun I shoot much (I've gotten pretty snobby about my air guns, and I really don't prefer using a bolt action when I have side lever guns available). I have only pretty recently gotten around to adjusting the trigger (which can be pretty nice on these Hatsans).
To me the Hydra is a simple gun, almost a truck gun but a little too pretty for that. And it is not an 'expensive' gun, especially when you can get a fairly new one for a good price like you did. I don't ever think I would put a regulator in mine. Instead I would just learn its velocities over the entire usable shot string and shoot it smartly in its OEM configuration.
My reasoning?
1) The cost of accessories can be incredibly high as compared to the cost of a gun. I have seen the Hydras come up refurbished on Hatsan's site for between $250-$280. So that ~$100 you will pay for a HUMA regulator is more than 1/3 of the gun's overall value;
2) While I think that HUMA's products are incredibly well engineered and highly functional, they can still be a whole bunch of work to install and adjust. I looked over the Hatsan installation instructions on HUMA's site and it seems like it will be a real PITA install, especially if you will need to notch the air tube and cut a slot in the threads of the valve body, etc. From the looks of the install, it could go bad and one could F up a gun pretty easily.
3) Even if the installation goes as planned, using an internally adjustable regulator (even if only tuning the gun for a single, specific pellet and speed) is a pain. The level of disassembly to access the reg, make small adjustments, re-assembly, chrono testing, and repeat as needed gets old real fast. For this reason I have sold most of my guns which don't have an externally adjustable regulator (or have an internal regulator, but come well set-up from the factory). They just take too much time to tune, when I would rather be out shooting instead.
4) If it were my money, I would take that ~$100 which you would use to buy the HUMA reg, and use it to start a fund to purchase a gun with an externally adjustable regulator, like an AV Avenger. You see those come up used on the Baker Airguns site for as little as $250. So that HUMA reg costs nearly half of what you could purchase a used Avenger for. And the Avenger gives you not only the external adjustability, but also the side cocking lever.
There is nothing wrong with an unregulated gun if used correctly, and some argue that the simplicity of an unregulated gun is a big bonus.
Just one man's opinion.
