These things have to be one of the biggest memes ever created. Not just in cycling, but out of every hobby in the entire world.

First, let's consider the advantages of equipping your bike with these
>Achieve the exact same pedalling efficiency as flat pedals (proven by countless studies)
>The pros use them... because... uh.. all the other pros are using them

Ok wow very convincing, now let's consider the minor downsides:
>have to buy expensive pedals
>have to buy expensive special shoes you can't use for anything else
>you can't even walk properly in the shoes
>takes longer to start from a stop
>takes longer to get off the bike
>can't adjust foot position while riding
>can't bail off the bike
>you stay attached to the bike in a crash