729 pounds test fee for the most stunningly easy flight test to fail. Less than 50% pass first attempt.
Couple of hours of aircraft rental, at some 6 pounds per minute to run the engines, to do the test with.
Not worth the cost at 80 pounds?
If the RANT disc saves you 13 minutes of flight time (or taxi time) by allowing you to figure out just what the hell is going on with those needles, then it's worth the money.