Firstly, it fits the camera very well. It's snug but easy to fit and fills you with confidence that it's going to look after the camera you've spent all your hard earned pennies on. Secondly, it's solid. So solid that I have complete confidence that should my camera be dropped any reasonable distance and not be unlucky enough for the screen or lens to land directly on a jagged rock, that the case would do it's job impeccably and it would just bounce straight off, keeping the camera safe and sound.
A lot of thought has gone into it's design. The button cut outs are perfect so that you have unobscured access to both the power button on the side and the record button on the top. The cage opens on the side for easy access to the battery and memory card door and on the other side the usb charging port can be easily accessed and the door removed if needed. The 1/4" threads on the bottom, top and side give even more versatile mounting options to the osmo action 4 (or 3) along with the ability to use the usual magnetic mount in either vertical or horizontal orientation. The cold shoe mount, unlike in some other cages, allows the attachment of most mic receivers or lights without obscuring the record button which is a massive oversight with other cages. It does add a little bit of weight to your camera so bear that in mind but if you're like me, you don't mind that weight to give that extra protection to your camera. Except for the plastic cage that comes with the camera that in my opinion offers very little protection for a considerable impact, any metal cage is going to add similar weight.
One thing to note is that I originally bought one of these from غ and the magnetic mount did not line up correctly so was not attaching properly and coming unattached easily. I returned it bit by then, the offer that had been on it previously had finished. I therefore found an offer to purchase directly from SmallRig and the replacement fit and worked perfectly.
I have no doubt that I have bought the best cage with regards to quality, versatility and value.