Simple to set up and does its job

The free version worked perfectly for a few substitution rules. The pro version allows an indefinite number of rules, and the price is very reasonable. Having seen the free version at work, I bought the pro version without hesitating, using it to rescue a 17-year-old site that embedded thousands of pictures from Wikimedia Commons and was completely broken when Commons changed the way it served images.

One small suggestion for improvement (which doesn’t detract from my five-star rating): it isn’t obvious to a new user that, when you add a rule, it isn’t actually added until you push the “Update Settings” button. Changing the interface slightly might eliminate some of the “Didn’t work” reviews.