Well, there are two entities that might object: Udemy and the owner of the brand.
Udemy only cares that you're not trying to sell this product to your students. So don't say "you can buy this at my website" or whatever. You can only sell stuff in your bonus lecture.
The owner of the brand probably publishes guidelines on what they consider fair usage of their trademarks, so you should read that first to be safe. Beyond that, you're getting into legal territory people on this board aren't qualified to provide advice on. There's a reason brands are usually blurred out on TV shows, but people post videos reviewing specific products all the time, so it seems like a gray area.
