npas allows to adjust fps on a gbb..
they are only trying to tell you is that GBB mags are expensive. in order to have the same amount as the people playing with you or against you mostly has AEGs that takes 100-500 shot mags. loading each one is also a pain when you have 5 mags each taking 30ish. So you are paying almost for another gun lol...tbh as soon as you play some rounds, you will start to see a 30rd mag is gonna be so bad just because unlike a real firearm, bbs don't really fly straight enough. So you will be firing a couple more shots just to get someone.
anyway, but GBBs do seem fun. Doesn't really work in the cold tho.
Probably most people suggest WE M4