Unlike the others here, I've had pretty good luck with Ribcage products... to as much of an extent as can be reasonably expected.
I first bought their kit to convert a Yi 4K+ to C mount and I somehow botched the installation, but they were willing to help me un-botch it in the end. Ultimately, I found that C mount lenses were extremely difficult to use with the Yi because...
The internal screen is tiny and not very high-resolution. This made critical focus nearly impossible, even when using a loupe.
There is no HDMI output option to use an external screen to check critical focus. It is possible to use an adapter to get composite output, but none of my external screens are composite...
More recently, I bought a pre-assembled kit with a Hero 7 Black. This is a vastly better experience.
The internal screen on the Hero 7 is much better-quality than the Yi and there is an option to digitally zoom in which is very useful for focusing. This is a little bit awkward, but works OK
The camera has HDMI output which can be useful for focusing if I already have another screen, but this has limits - in video mode, the HDMI output is very laggy. In photo mode and timelapse mode it's very fast... but it is pretty awkward to have to change modes constantly in order to focus.
Image stabilization is not very well-optimized for longer lenses so they end up still feeling sort of shaky
I have found that a number of D mount lenses have sufficient coverage for the 1/2.3" sensor in the Hero 7. I'm still looking for a wide angle option without a hard vignette, but lenses in the 10mm and longer range seem to cover sufficiently... which is at least enough for a very minor telephoto with around a 10mm lens. I'm hoping, though, to find a 5mm or so D mount lens with enough coverage. Unfortunately, D mount lenses aren't super common on the used market. In this regard, the 1" sensor (2.7x crop) in the RX0 would be very strongly preferable.
Whatever the Ribcage looks like internally or how much electronics purists turn up their nose at it, the camera feels plenty solid from the outside and mine has been banged around quite a bit. It still seems to be doing alright.
The Hero 7 has HEVC at around 78 megabits/second. I would be curious to compare its output vs the RX0 with semi-cruddy HEVC-S at 100 megabits/second. In addition, the Hero 7 can handle 60 fps in 4k where the RX0 is only capable of 30 fps. On the other hand, the RX0 can output 4K at 422 for external recording if you don't mind bulking it up a little bit.
The Hero 7 also has 2.7kp120 and 1080p240 options and I think both can be used continuously. The RX0 has 1080p240. Assuming that it's like my RX100 V, this mode will be limited to only a few seconds. I'm not sure how much any of this matters since the quality of all of the above is fairly mediocre.
The RX0 has Slog. The Hero 7 has ProTune. I think both are usable enough with moderate dynamic range scenes.
The RX0 almost definitely will work better in low light than the Hero 7 - and in addition, it's possible to use a speed booster with the Micro 4/3 mount where I am not aware of any decent-quality C mount speed boosters.
In the end, I thought about buying the Ribcage RX0... but ended up deciding it didn't have enough advantages over the Ribcage Hero 7 to make it worth the swap.
This is reminding me that I want to use the Hero 7 variant more... I suppose I'll make an effort to bring it with me the next time I go shooting.