It cost me $100 when I bought it like a year ago. It is awesome and works really well. Basically you plug it in the outlet that your router goes into and then connect the Ethernet to the router And then plug in the other connector into an outlet next to your computer and then plug the ethernet into your computer. It is wireless ethernet essentially.
It worked really well for me, the reason why there is red marker on one of them is because I was using two in the house and I wanted to mark which one went with my computer.
Works perfectly, I'm only getting rid of it because I am moving and will have my computer right next to my router where I moving to so I don't need this anymore.
Works perfectly!