It's my understanding that the pros don't use this. If you don't have enough torque, you're probably doing it wrong, and would soon be out of gas even with more mechanical advantage. Shift down, pedal faster.
It all comes down to how good the motor (legs+lungs) is.
Non-circular gears change the gear ratio as you pedal. It effectively shifts down in that part of the pedal stroke where you have the least strength. Since the bike doesn't slow down, your feet must speed up. Then, when your feet swing around to where you have more strength, it effectively shifts up.
My argument is, if you are pedaling at the limit of your strength, you are in too high a gear. Shift down and spin your feet faster. You'll use less strength, and more aerobic capacity, enabling you to maintain an equivalently high power output, but for longer. It's easier to run a marathon at a constant speed than to sprint 100 m at a time, taking walking breaks to maintain the same average speed.