Check out Leo's videos on YouTube were he is testing the muzzle flip of the TSO and spring combinations. He using a 40, but the same principle applies to testing your 9mm. I've contacted CZ USA, UB, CZC, and, CGW, all of these companies do Not recommend using under 12lbs springs ( unless the gun is compensated ) as they have told me there are to many failures.
My TSO 40 recoil spring was super tight and was hard to remove when the pistol was new, but now after about 1000rds seams to slip off of the guide rod easier.
I'm shooting it with the factory 16lb recoil and 20lb main spring at 170pf and have had no issues, but I'm going to try a 14lb recoil and 15lb main.
When this gun ejects, it throughs the cases 15' !!! I usually have to go pick up my own brass as most of the people's 9mm brass falls at their feet.
https://youtu.be/tcT3i4269Bohttps://youtu.be/4hDk6buPRKw