I'm pretty disenchanted with lens adapters. I've never found a single one which wasn't a hateful, error prone thing. I think the issue is that tolerances on the imaging chain are pretty damn tight and it doesn't take much to screw something up.
I've got a speedbooster EF to m4/3. It sorta works, but the communication with the camera is a little iffy- once in a while it'll decide the lens isn't correctly mounted. Using the screw thread on the booster when on tripod helps counterbalance the weight on both sides, but it still cannot be relied upon to just work in the way a native lens on a native lens mount can. Plus there are focus shifts- just enough to wreck critical focus with my Tamron 11-16 which has a hard stop an infinity, preventing it from quite hitting infinity focus on the GH4, sometimes. (It seems to be temperature dependent- if I was going to continue using that lens I'd see if I could get the hard stop removed just to give me a couple of extra degrees past infinity, just in case).
AF doesn't really work with most adapters (although I gather the new Kipon improves on this- but it isn't a speedbooster, so forget wide angles).
I've got a cheap Chinese adapter which physically mounts the lenses, which it does fine, but no control over the lens at all.
Even the official Panasonic 4/3 to micro 4/3 adapter I have on my Olympus 12-160 mm is prone to occasionally deciding to pretend the contact has been lost, requiring unmount and remount of lens and adapter- which is easy enough, but not something I've ever needed to do with a native lens.
Since I like the GH4's small size, ergonomics and video capability I've given up and just bought Panasonic 7-14 mm, 12-35 mm and 45-200mm. I'll probably complete the set with the 35-100 f/2.8 or one of the Olympuses and be done with it. I do like having a full lens set in a trigger case on the side of the rucksack!
Cheers, Hywel.