I've noticed my stick also becomes very warm, ( close to hot ) but cant really go as far to say its hot,
Not sure if it is a good idea in regards to the stick needing updates etc., But I have started cutting the power to the stick when not using it for long periods of time when I am out all day or when I go to bed at night.
Just for the reason to give me peace of mind just incase there is any possibility of it becoming a fire hazard, But I don't believe or think it is a hazard as others have said you will get a overheated warning message on screen.
Your best to plug the USB power cable into the USB port of the TV.
That way when your TV turns off the stick does too.
But yes it’s 100% safe otherwise it wouldn’t be sold to the point of being out of stock on the NOW website.
Just a thought, it may be beneficial, to as well as taking Gavs advice, for you to get yourself a small desk fan and use it to blow air constantly across your NOW stick, thus keeping it cool.
It's a technique I use to keep my small, constantly on, electrical devices cool and this may also work for you.