Starting with three wheels allows great stability compared to a standard bicycle. OK, so the trike doesn't generally fall over on it's own accord, but my feet and or legs don't always follow directions... so the next step for some is how to keep your feet up off the ground and on the pedals.
In an emergency, you could use duct tape, which is fine for those who have hair free feet. For others there are several pedal configurations that allow many people to use a recumbent trike that could not balance and use a standard bicycle.
The Crank Shortener makes it possible to freely adjust the length of the crank arms, e.g. for riders with legs of different lengths. The new forged part not only looks nicer than the previous version but is also more robust and can even be properly aligned on offset crank arms.
These pedals can help people with severely limited mobility slowly regain their flexibility and strength. The trick: pedaling is possible with very little bend to the legs. The pedals can be adjusted to allow for more movement as leg strength returns, creating a beneficial training effect.