The Guntec USA AR-15 Slim Line/Micro Cone Flash Can is considered a flash hider.
The Guntec USA AR-15 Slim Line/Micro Cone Flash Can is a muzzle device that directs the muzzle flash and concussion forward away from the shooter. It is not a suppressor. However, certain states prohibit the use of certain muzzle devices so please check local laws and regulations in regards to your ability to own the Guntec USA AR-15 Slim Line/Micro Cone Flash Can. The guide below will also provide information regarding different types of muzzle devices.
https://www.opticsplanet.com/howto/how-to-select-a-muzzle-device.html
The Guntec USA AR-15 Slim Line/Micro Cone Flash Can does not need to be timed and therefore does not require the use of a crush washer.
For a 300 Blackout rifle your will need the 7.62 model of the Guntec USA AR-15 Slim Line/Micro Cone Flash Can. Be sure your barrel threads match the threads of the Guntec USA AR-15 Slim Line/Micro Cone Flash Can which are 1/2x36 for model number CONE-FH-S-9.
Yes, the Guntec USA AR-15 Slim Line/Micro Cone Flash Can model number CONE-FH-S-9 is designed for 7.62x39. So this model will work as along as your barrel is threaded 1/2x36.
The manufacturer doesn't state if the Guntec USA AR-15 Slim Line/Micro Cone Flash Can is full auto rated. I recommend contacting the manufacturer in regards to that information.
The Guntec USA AR-15 Slim Line/Micro Cone Flash Can was not purpose built for a 7.5" AR. It will fit and function inside any rail that has an internal diameter larger than 1.25".
No, you can not.
Yes, providing you get the correct thread pattern.
Yes, the 1/2x28 will work well.