I got a 2x teleconverter to use with my 70-200mm f2.8. Using zooms with this Canon has awakened something expensive in me and now I want big zooms for everything.
I have learned that even 400mm isn't enough for taking pictures of birds. Have I mentioned I like birds now? Birds are good.
I've read a criticism of this extender that it's basically unusable. Unacceptably soft focus, slow. It's obviously softer and slower than the 70-200 but then most things are. It's still perfectly usable, in my opinion. If I were printing billboards it'd be problematic but for this website, Instagram and small prints it's totally fine. Considering I don't have £6,000+ for a 400mm prime, I guess I'll make do with this unacceptable £260 shortcut.