I currently own the Rokinon 7.5mm fisheye, which I love but I am tempted by the other options. I made a pro and con list below but would like opinions on factors I may not have considered. I will be using it for shooting mostly landscapes and stock footage. I am currently shooting with a GX7 although not attached to the m43 format. All three are reasonably sized and price difference is not a huge factor so image quality and practical usage is the biggest concern for me. Any input, especially from people who used all 3, will be greatly appreciated. Thanks! Rokinon 7.5mm Fisheye Pros -Wider aperture, shallower DOF -Slightly wider FOV, can still de-fish for narrow FOV if needed. Cons -Harder to frame shots (horizon needs to be centered) -Can't use filters without modification Olympus 9-18 Pros -Zoom is ideal for run and gun video. -Rectilinear for easier framing. No need to defish (Almost always prefer defish images) -Works with Cokin A filters (for Grad ND and Polarizer) Cons -Slower aperture. -Reviews seems less favorable to 7.5mm fisheye. GoPro Hero 4 black Pros -4K video (worth more $ in stock footage and future proof). -Standalone/backup camera. Not format specific. Can use both simultaneously. -Can use as action camera. Cons -No LCD (will sync with phone for framing) -Need modification for filters. -Limited photographic functions (i.e. manual controls, use with strobe).