Mine is a factory MB cover.
Here are some pix and the associated problem areas.
From the rear you can see this does not cover the antenna, you unscrew it before covering. Pobably a much better idea anyway.
On the right side if you look at the mirror you can see where it has started to tear.
It is a slightly tight fit and had I used more care from the beginning I may have been able to avoid the tear.
The gromets on each side are a bit flimsy too. My outer ring is split and will fall off if I don't keep an eye on it.
I use a bungee to secure the middle of the cover between the gromets, tossing it under the car. I also use a couple of small bungee's on the front of the cover (one on each wheel) otherwise a little wind will find your cover either beating up the car, or the cover off in Kansas somewhere with Toto.
Also, the wee bit of elastic along the lower edge is no match for even the lightest of wind, so if using in a garage fine, if using in any sort of wx at all, some bungee setup or some other means of securing is needed.
I haven't found any aftermarket covers yet, and this one fits so well that I'm inclined to buy another one and call the wear & tear a cost of leaving outside once in a while.