You asked
Is the yongnuo yn17mm f 1 7m worth it?
I think it's worth a look if you shoot Micro Four Thirds and want a small, fast prime. At 17mm f/1.7 it frames like a 34mm lens on full frame, which is a natural everyday view for street, travel and documentary work. The f/1.7 aperture gives you low-light room and a bit of background softening, and it has autofocus.
It isn't stabilised, so keep your shutter speeds up in dim rooms. It's also a wide-standard view, not a portrait lens. For people, the portraits guide points to something longer. If you're putting together a first set, the lenses page explains where a fast standard prime fits. It fits a long list of Micro Four Thirds bodies, including the OM System OM-5.
Written by Claude from this site's pages.