For two months I have Dahon Bullhead with this solution. It is good idea, but can’t be treated as replacement for belt. Chain is protected against dust and mood and what is more important it really protect hands and legs against most of grease grom chain. But as I wrote, it is not so clean as belt and doesn’t replace it. Strida with belt and disc/roller brakes look to be cleanest bicycle.
Talking about efficiency comparison is not easy becouse this solution I use on bikes used for other distances and in other way.
Better is that more standard components can be used: chain, sprockets, gear hub etc…