Hello @Llamudos
1. cant comment on this as i have never attempted it but i can only imagine it adds more noise to your gearbox, ive always recommended getting a stronger spring and cut down if need be.
2. due to the barrel length the fps can vary due to the air in the cylinder and how far it has to push that bb out the end. longer barrel = more air required.
3. they are generally good products but in the case you are just testing for site chrono, most sites will still want to chrono your gun regardless of what you say.