Currently, this teleconverter can be picked up for around £275, which isn’t quite bargain-basement territory, but is still less expensive than Canon’s EF Extender 2x III, which costs £300 The extender comes with a compatibility chart which essentially lists all of Canon's posher telephoto primes and zooms from 135mm f/2 up. Extenders also multiply the f-stop. The 135mm f/2 becomes a 270mm f/4, the 70-200mm f/4 becomes a 140-400mm f/8. .

canon extender ef 2x iii compatibility chart