The flip-flop I used was/is firm(they probably wouldn't have been the most comfortable to wear), there has been no breakdown in close to a year, with multiple track days on them. I did use a long screw/nut combo and had to drill into the metal pedal and tightened it all up. Since 3 screws are used and its all tightened up quite a bit, there is absolutely no slop/flex in the pedal under hard braking (the last thing I want when coming down from 120+mph with only the left half of my foot on the pedal).
for the clutch pedal I drilled though the rubber cover and through metal pedal and put the supplied screws through it with with lock nuts on the reverse.
Just thought it was a relatively low cost option to my dilemma that didn't involve placing a cover that effectively decreased the distance between the accelerator and brake