OVERVIEW:
For STUDIO work (with a heavy tripod) I still recommend this camera. For on-location work, I don't. The reason I still recommend this old camera, is you can get decent results from the GH4 (especially with my custom, lens-sensor settings) but the lack of IBIS makes it a big bother to use in the field, because you need either a big tripod, or a gimbal (neither of which I use or like to carry, anymore). I have been testing camera alongside the G7, GX85 and G85, and the shirt version is I would say to buy a Panasonic G85 before a GH4... especially if it's your first camera. (Another reason I don't recommend the GH4 as a first camera is that the screen is so inaccurate you need an external monitor to judge exposure and focus (the GX85 and G85 are much better).

MAIN POINTS:
PART 1: IS IT PORTABLE?
PART 2: IS IT AFFORDABLE?
PART 3: IS IT COMMON?
PART 4: HOW’S THE QUALITY?
PART 5: IS IT EASY TO USE?
PART 6: NEEDS ADD-ONS?
PART 7: WHERE DO I BUY?

PART 1: IS IT PORTABLE?
No, because the sensor isn't stabilized, so you also need to pack a sturdy tripod and/or a gimbal.

PART 2: IS IT AFFORDABLE?
Yes! It's a bargain, if you don't mind the lack of IBIS...I totally recommend it for studio work, especially because it's so inexpensive you can buy it and then leave it set up in your studio (then take your other cameras with IBIS on-location).

PART 3: IS IT COMMON?
Yes, most likely because it sold so well initially (it was the only 4K capable camera in it's price range for a long time).

PART 4: HOW’S THE QUALITY?
While it takes learning the sensor's limitations, it is capable of creating an excellent image (for video purposes especially). The screen isn't very accurate, and the sensor has noise issues, but as you learn what it can do, you'll probably be happy with the quality...as long as you have enough light because the low-light capabilities aren't good (that's another reason I only use it INDOORS, with added lighting).

PART 5: IS IT EASY TO USE?
No, but that's just compared to cameras with IBIS (because you don't need a tripod or gimbal with those). As far as the GH4 menu system and other things, it's pretty easy to learn. It does have more advanced video features (and more complex menu systems) than lower-end models like the G7, G85, GX85, etc.

PART 6: NEEDS ADD-ONS?
Yes, it needs a sturdy tripod, or a gimbal (because it doesn't have IBIS). An example of why this matters (to me) is that I was shooting with my normal travel-sized carbon fiber tripod, in an OUTDOOR situation, where there was wind...and the videos were unusable (shaky footage, etc.)

PART 7: WHERE DO I BUY?
I've purchased it 2 times, both from local people (from OfferUp) and they were really good deals! One interesting things is that this camera is older, but people really like them so a lot of them were taken care of, and are in pretty good condition!

CONCLUSION:
In conclusion, I should mention one more reason why I only like using the GH4 INDOORS (in the studio, especially). It's because the AF isn't very good, and I can overcome that in the studio (by pre-focusing a manual focus lens, taping it, and leaving it set)...so that's pretty much the way I use it. I'm not saying it's impossible to use OUTDOORS, but it's certainly not as easy to use as a newer camera, that has IBIS.

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These reviews are just my opinion and are focused on my Q.P.A.C.E. packing method, so they're not comprehensive. I wrote these mostly to help me remember what items worked for my KIT PLANS (and which didn't). If I said anything negative I apologize, as these products still may work well for you in your situation, but they were not Q.P.A.C.E (Quality, Portable, Affordable, Common, Easy-to-Use) enough for my budget filmmaking KIT PLANS.