Here's a stark contrast between two different gimbal stabilizers. One is the Nebula 4000 - a handheld pistol grip style 3 axis gimbal for small cameras. The other is your typical 3-axis gimbal frame. While the goal is to have the smallest stabilizer possible, there are cons to going with something too small for cameras like the GH4 and A7s.
Dave Dugdale over at LearningDSLRVideo.com has recently picked up the Nebula 4000 to use with his GH4 camera and has been sharing a few different tutorial videos. Here's the first video showing his initial setup process.
Granted that with some practice you'll be able to balance your camera faster. You may also get better results with a lighter or shorter pancake lens instead of the 12-35mm F/2.8 on the GH4. Obviously the tiny form factor makes this a great compact tool, but it also comes with many cons. The pistol grip design will make low mode shots quite awkward, and a GH4 sized camera will have limited tilt up/down movements before it starts hitting the back roll motor. While I think the Nebula 4000 may be a well made product, it might be best used with smaller cameras (or at least ones with very compact lenses) and when you don't need to re-balance your camera setup.
The DIY 3-Axis Mini Gimbal Frame Project
In Dave's video you'll notice he may reference a project gimbal i've been working on. For a camera the size of a Panasonic GH4 or Sony A7s, I personally feel there's a minimum size that would allow you to get the most of your camera while still remaining portable and compact. Over the last year, I've built a couple of mini gimbals from scrap parts simply for personal use. Just recently, I decided to take notes of everything I wanted to have in a compact gimbal and had a custom designed frame machined from aluminum. Here's a look at an early prototype i've been using for several weeks with my GH4.
[Update 12.23.2014] These are unreleased videos I shot a while ago as I was documenting the process. I decided to release this today that shows some additional information.
Another recent balancing video
So far from my knowledge, this DIY Mini Gimbal frame has the potential to be the most affordable compact system for GH4, A7s, or BMPCC cameras that allows use of a Manfrotto quick release, provides access to the HDMI + Audio ports, and offers tool-less adjustments for quick balance. So far i've only made 4 of these gimbals and i'm working on a 'DIY Build Video' to show how anyone can wire up their own gimbal. The idea is that hopefully a few more of these frames can be made. If you're interested in this project leave some comments and keep following the blog.
Cheesycam DIY 3-Axis Mini Gimbal Frame for Panasonic GH4 Sony A7s