According to GG's Bombing the Reich, the WGr210 rockets are a good asset to disrupt enemy bombers formations (they will launch their rockets, and probably shot down some of them, but their real effect is the disorganization of the bombers formation). Once disrupted and disorganized it's easier for the rest of the interceptors to shoot down a bunch of them.
The problem is that the planes carrying WGr210 will have their performance downgraded (weight, aerodinamics, etc). So, interceptors will be more vulnerable to escorts prior to launch their rockets.
As an advice, you can try to use them against unescorted formations (deep in Germany) following the advice that you have already received, or you can use them with your heavy fighters (Me410 i.e.), or you can use them only in a small proportion of your interceptors.
In the theory, if any of these rocket armed interceptors survive to the escorts and launch their rockets, this will help the rest of the interceptors to shot down disorganized formation of bombers... at least in the theory.