The speed limit warning beep is fine if it's just once on speed limit update or when you go above, so at least you can make your own judgement.
Not sure what feature you have that flashes the BRAKE! warning, only I one I know of is the collision detection one that makes a warning sound that is quite reliable.
Ya, people follows where the content is, also people are lazy, so if you still post on x your followers will not migrate and you will see worse numbers on the new platform, but if you fully stop posting on x your followers will follow you to the new platform (you will not hit old numbers but those are inactive followers anyways).