These lenses are not made for teleconverters. You are better off cropping in after.
Thanks by the way they say f8 teleconverters work fine
I'm speaking more to the end of practicality, versus what you technically *can* do.
There is two ways of going about getting more reach from a lens: Digitally crop in, or optically extend your reach.
In the case of a 150-600 or 200-500 lens, you really are already getting all you can out of the lens. These lenses do not fully take advantage of a 20+ megapixel sensor. This means that cropping in digitally will produce approximately the same result as using a teleconverter.
With something like a 600mm prime lens, a teleconverter makes sense. It will resolve so much detail for your sensor that a teleconverter will help. This isn't quite the same with a superzoom.