My experience with the lens comes from using it with Olympus cameras (EPL5 and OMD EM10 III). I bought the lens because my previous telephoto lens, the Olympus equivalent, gave up after 4.5 years of use - so I can answer the question for those who want to get a cheap telephoto lens for MFT.

Features:
* Small size: incredibly small for a lens that reaches 300mm equivalent, when collapsed it has the same size or even smaller than the kit lenses for APSC DSLRs. It is also smaller than the Olympus equivalent.
* Image stabilization: despite its small size, the lens is optically stabilized, a very useful feature for Panasonic cameras that do not have sensor stabilization like Olympus. It manages up to 1/4 second exposures at 150mm without much blur.
* Sharpness: Both lenses are quite sharp, although I think the Olympus lens is sharper at shorter focal lengths.
* Brightness: Although both lenses have the same aperture at minimum and maximum focal length (4-5.6), the Olympus lens was brighter at intermediate focal lengths, for example, f/5 on Olympus was at 100mm while the equivalent on Panasonic was at 70mm.

Focus:
I leave the focus separately because it's another story. Although theoretically the lens is compatible with Olympus cameras, the experience using it with the E-PL5 was almost unacceptable in terms of focus. The lens refused to focus at focal lengths below 100mm(!), especially in low light or cloudy conditions, and focusing had to be done manually many times. The experience with the Olympus OMD EM10 III, which has the next generation processor, was better, almost normal, as it does not face such intense focus problems.