The Cycliq FLY6 is a solid piece of kit that straps onto your seat tube, and is designed as a "turn on and leave it" device that continuously records video footage of the view behind. The footage is wide-angle to capture lots of the periphery too.
You use a velcro strap to attach the camera to the seat post. Technically, the camera attaches (with a 1/8 turn) to a mount that takes the velcro strap - but I have never removed my camera from its mount. Instead I just undo the velcro strap when I want to move the camera between bikes. The camera comes with two rubber shapes that allow the camera to be attached to either a round or an aero seat post. When mounted to a round seat post I find that the strap has to be pulled very tight to stop the camera from slipping around.
Video quality is very good and also adjustable - so you can have HD quality if you like, or switch to the lower quality SD format to capture more footage on a single memory card. You need a computer to get the video off the camera. This is easiest via the camera's USB-C port, using either a USB-C to USB cable or a straight-through USB-C cable - depending on what your computer has. Alternatively, if your computer has a memory slot, you can also remove the memory card and slot it into your computer. Either way, you can them browse the video files on your PC and import them into video editing software if desired.
The camera is designed to capture "incidents", by locking the video file so that it can't be over-written until the SD card is reformatted or the file is manually deleted. I've seen these from time to time, but they never seen to correspond to anything important (such as a close pass).
The FLY6 can talk directly to your Garmin cycle computer, as it appears as a light in the sensors list. By connecting it you have a bit of control over the light, directly from the Garmin head unit, and can also see status information like its battery life. I don't actually use this feature, as the FLY6 seems determined to stay turned on and recording when the Garmin is within range - so if I want to turn it off for whatever reason, it annoyingly turns straight back on!
One very important caveat with the Fly6 is that its USB and SD-card access area is on the top of the device. This area is protected by a rubber cover that does a great job of keeping water out - but the device can fill with water (and hence become bricked) if the rubber cover isn't in place in the rain. On a long ride I needed to charge the Fly-6 on the go, so had a battery connected via a USB-C cable; fine when the weather was dry, but fatal when it started raining (and I'd forgotten that the cable was plugged in). I later asked the company about it, and they very kindly sent out a replacement for the price of shipping from Australia.
The FLY6 is a well-built and durable unit, performing as expected in all conditions. Video quality is great too. Just be aware of the limited battery life - and don't charge it up when it's raining!
As far as incident capture goes, I'm in two minds about how satisfactory it is. On the one hand I've submitted several close-pass reports to the Police, yet on the other hand only two have resulted in the driver being spoken to or warned. The reporting procedure in my region is also very time-consuming; it's treated as a dashcam report, and I need to fill in a lengthy form which commits me to testifying in court if necessary. When these incidents only really need the driver being warned about their standard of driving, this bureacracy is quite tedious and pointless.
My more fundamental experience with crashes is that I have always been hit from the front or side, so a rear-view camera isn't really much use in these circumstances. So I would actually favour a front-view camera (potentially the Cycliq FLY-12) instead. Having a two-in-one mounted on the end of my handlebar would be my favourite, but I don't think that these exist.