From personal experience i think the CS absolutely sucks ! Bought a pistol when it arrived was obviously second hand/a return tried contacting them and after several unanswered emails finally got a reply which basically said don’t believe you so tuff !
A very good friend had a sniper upgraded buy them asked for it to be between 450-480fps , it arrived trieded it just once , it made a horrendous noise when fired and didn’t work again (basically it had imploded) and on further inspection by the guys who know there way around snipers (he didn’t hence paying Z1 to do it) at our regular site they proceeded to identify several ‘up-graded’ parts that were actual standard parts even though they’d been paid to replace them and they also said the spring fitted was way too powerful for standard parts hence it imploded !
So me I only use them when I really really have too because I can’t get x,y,z any where else , and I CERTAINLY wouldn’t use there tech service either !