The Panasonic Leica 12-60 F/2.8-4 is a great lens for the Panasonic GH5. Mirror Lessons and Camera Hoarders completed their reviews of the lens and both like the lens, but Mirror Lessons seems to be more in the Olympus camp preferring the Olympus M.Zuiko 12-40 f/2.8.
Panasonic Leica 12-60 F/2.8-4 B&H Photo / Amazon / Adorama
Olympus M.ZUIKO 12-40mm F2.8 PRO B&H Photo / Amazon / Adorama
Panasonic GH5 B&H Photo / Amazon / Adorama
Olympus OM-D E-M1 Mark II Amazon / B&H Photo / Adorama