As Sceptre said, it's about the MiG-15, not the GAR-8.
As for the performance of the GAR-8, I have found it to work quite well. It's after all the first operationally used heater in the world, so don't expect it to perform like an AIM-9X with JHMCS. Pull less than 3 Gs when firing it, and for locking on, I've found a good method is to cage the sight and use it as a sight for the GAR-8s, approaching a target from behind. For smaller planes, you simply have to get quite close in.
I've had no issues shooting down P-51Ds and FW-190s with the GAR-8.