Convertible skates are such a good idea. Snap them to your shoes, pop them off at your destination, no need to carry a pair of civilian shoes with you, no need to sit on a curb or fireplug while you change out of your skates. But why do they always suck?
I owned Metro Blades
And I remember other failures. Xsjado used to sell one, for example. And now Cardiff has entered the market. http://www.cardiffskate.com/products/cardiff-skate-s1
The skate has four wheels, arranged in a diamond pattern, which adds to stability but must make turning much harder, and the things look huge, almost certainly harder to carry around than my normal commuting skates.