The problem with using wide angle lenses on M4/3 is with there widest apertures, with the super wides the problems increase further, with widest apertures often being between f3.5 to F4.
This 19mm widest aperture is f3.8, however it can focus remarkably close, making this lens quite handy when very wide apertures are not needed and its a worthy lens on the street, the close focusing ability compensating for lack of a really wide aperture.
This lens compares well against the Nikkor 20mm, optically this lens performs just as well.
This Vivitar series 1 lens was manufactured by Cosina.
These can be picked up quite cheaply, expect to pay between £20/£30
(For this series I first opened the lenses fully, then closed and set the aperture by just one full stop)