I bought affordable skins for all my most-used guns with StatTrack, so I wasted about $40 I believe. Half of them was on skin opening sites, trying to hit jackpots, but getting shit.
Just buying the skin you like for the gun you use mostly is better than trying to open it. I got 12 StatTrack skins (almost all are Factory New), they look cool, and I honestly don't feel like I need to get more expensive ones.
But what some people above said is true --> I play like shit if I'm not using my StatTrack weapons.