I do not think so. Crack is just cosmetics and almost do not affect performance. Of course if price is a bargain than why not have this nice dish. I also think that crack can be easily fixed, so, no one will ever notice there was one.
Not really you must reinforce it well, the signal on an off dish is not affected on the bottom, that is why you could have snow 5 inches up from the bottom and not affect it, but the top part is