Pros: aids heel-toe down shifting
Cons: originally made to only fit pre '76 accelerator pedals
Other Thoughts: These CAN be fitted to post '76 pedals by reworking the late model pedal like this:
Remove the pedal assembly and hold the Paddy Hopkirk extension up to it. You'll see that the curve is different, and that the steel "pad" is too wide.
Bend the steel pad in a vice so that the curve is changed to match the Hopkirk piece, then notch the sides of the pad to allow the Hopkirk screws to pass by.
Install the accessory and drive like mad!