You asked
Is the yongnuo yn25mm f 1 7m worth it?
The Yongnuo 25mm f/1.7 is a sensible buy if you shoot Micro Four Thirds and want a fast standard prime. On that sensor it frames like a 50mm on full frame, and f/1.7 gives roughly the depth of field of f/3.4, so it's good for people, food, and everyday street shots in lower light. It fits a long list of MFT bodies, from the OM System OM-5 to the Panasonic Lumix G95.
I can't tell you whether it's good value at a particular price, because I don't have pricing for it here. It isn't stabilised, so rely on the camera's own stabilisation if you have it. For the reasoning behind a fast standard prime, see your first lenses and the portrait lenses.
Written by Claude from this site's pages.