I have gh3, also the slr magic 12mm 1.6 and slr magic 25mm 0.95. I love all of them. I use the 25mm more.
if you go to this guys videos and do a search or look at his earlier stuff https://www.youtube.com/user/darwinfish105/videos
he has some videos with the 12mm, the 25, also the 17.5mm on the gh3