Ok, having labored the decision of acquiring a Korg Zero 4 mixer all those years ago for its all in one solid integration of professional digital and analogue mixing features against other less integrated pro DJ hardware solutions, I haven't actually been able to let go of my Zero4 after the many years I've had it so far. It is very much so still quite advanced against many other alternative full sized mixer solutions that don't even come close, and it still leaves much of the competition standing even after all these years. But it was time to think protection for old trusty. It seems there are no reasonably accessible custom fit solutions as far as Zero4 flight cases go. But then one day I stumbled across a "Korg DJ mixer bag".  Now to begin with I was a little dubious as to any major potential design flaws it might have, such as the fact that it wasn't a hard case although a relatively sturdily constructed nylon weaved bag. My main concern was the potential for broken pots and snapped sliders.  

I hate to dump on this Korg bag as a product, but despite the fact that it’s a custom official Korg solution specifically designed for transporting Korg mixers I found that it is a little difficult actually getting the Zero4 mixer into the bag. It might be better suited to Korg's more compact full sized analogue mixer range. Although having said that with a little careful effort it will snugly accommodate a Zero4 with absolutely no room to spare around the sides at all as it required me to carefully slowly edge it in as the sharp metal corners of the Zero4 mixer would catch the corners of the bag. I could maybe see how this might cause the bag to rip with regular transportation and actual need to use the mixer over time whilst taking it out to use and packing it away again.

Other then that there's also room to fit a 17" laptop in the zip compartment in front of the main mixer compartment too, however I'd recommend that you have some sort of protective sleeve for your laptop as the interior of the laptop compartment (if you're not actually using it for something else) is quite spartan with no kind of padding at all. I'd also recommend that if you do use it for toting around a laptop along with a mixer that you also make provision for adding additional protective padding on top of your mixer to take any potential knocks that might cause your laptop to snap or break pots and sliders under it without the extra improvised padding.

Another downside is that there isn't any specific custom compartment on the bag for carrying a pair of monitoring/DJ headphones. 

Other then that there are two smaller compartments at the front that will comfortably fit all your cables and charger that you might need for your mixer and laptop.

As far as straps go you got a standard shoulder strap and  carrying handles. Concealed at the back of the bag there's a another zip compartment that conceals additional straps that allow you to carry it like a backpack. 

General opinion

In using this bag you'd still have to be very careful whilst transporting any of your gear in it. There just isn't the same piece of mind that you might get with using a custom cut foam lined pelican case or sturdily constructed foam lined custom cut flight case. But having said that it is the only custom light weight solution I've found that will allow you to carry your gigging/audio production essentials on your person as hand luggage.  Some protection is certainly better then no protection I guess.