Maruzen MP5KA4 upgrade help
 

I just purchased this gun and I am wondering about upgrades which are available and if anyone has any experience with them. I will only be using 134A gas because I havent heard anything good about green/propane use in these guns. The upgrades in question are;

- Tanio Koba Kick Booster piston
- RCC recoil spring set
- Guarder loading muzzle (do I need it for 134a use?)

If you have any experience with these upgrades then please let me know the pros and cons of them. Any help would be greatly appreciated.