Friends have used things like that and they leave scratches & marks when you finally remove them. I'd avoid them & just make sure you buy a decent sleeve or something like that to protect the computer when in your bag.
Don't put that ugly piece of crap on your beautiful Mac. Believe me, you'll be heartbroken when you remove it and see all the damage it left behind. Dirt gets in and causes scratches, then the clips eventually chip the edges. Get a good sleeve and some good old fashioned common sense. 😉