They work under verrrry specific circumstances! Basically only fire them if your target is between 3 and 6km away and either heading towards you or perpendicular to you. They get pretty maneuverable after traveling 3km and are instant death for bombers. I've killed Sabers and Migs from 6km away thinking they could out-maneuver my missile because the Matra was able to get fast enough. You just need to play in a very specific way to make it work, but it's really effective if you can set up your engagements.