Another way to see it - They are not charging you for the use of the Joey. They are charging you for gaining access to programming in another room. There are ways to spend some money up front and have no monthly fee. You can connect directly to the Hopper with another cable that must reach where your second TV is, and then watch whatever channel the Hopper is on. Or you can get a Slingbox and watch whatever channel the Hopper is on. There are more exotic ways that will still result in only being able to watch the channel the Hopper is on. To watch whatever channel you want in the second room you need to pay the $7 and use a Joey, theirs or yours.
One advantage of buying your own Joey is if the room is not always used, like not for a month or months at a time you can turn off the service or turn on the service in that room. If it is their Joey and you turn off the service to that room you have to return the Joey to them. otherwise using their Joey is the way to go.