The biggest complaints seen with crossman are these:
1. The fills are inconsistent or have duds.(I have never encountered this)
2. The CO2 is dirty. After sustained use it leaves a black residue in the gun. Also it has a weird smell.
3. The 12g casing is inconsistent in length. They have differing lengths and can stretch out the 12g seals in the gun. Oddly this make leilands look bad, because they are slightly shorter(but they are very consistent) so they will leak if you switch from crossman. This problem really only affects lever and dropout changers since bucketchangers always clamp down regardless of length.