"I'm sorry, but I think you need a new cover -- the current one is awful. I literally could not bear to leave the browser tab open long enough to read the description."
Why beat around the bush? If you feel you must distribute your advice at all, that is...
...
Seems to me the only issue is how to be polite about it. And I'm sure there are better politeness experts outside MR -- possibly on the political boards.
