Funny thing about reviews. They only use a single lens. The specs vary from lens to lens and body to body. You have no way of knowing where they land in the spec ranges or where the test body lands for that matter. Lens sample archives are better. But even then, you find issues since lower cost lenses draw less capable users who then post less competent sample work as compared to threads on more expensive lenses. This can lead to a false belief of inferior quality on third party lens threads.
The only real way is to get the lens, put it on your camera, and see what you get. So buy from places like Adorama who have a liberal return and exchange policy. Then you won't have to worry so much. If you get a lens that doesn't deliver the expected results, you can send it back and buy something else.
On a crop camera, the 55-250 takes advantage of the fact that the image circle doesn't need to be as large. It can focus extremely sharp on a smaller spot by moving the rear glass back further into the camera body closer to the sensor. This allows for an extremely sharp image at a much lower cost than is needed to produce the same sharpness on the larger image circle needed for a full frame camera. The down side to this is that it can't be used on a full frame camera because it protrudes too far into the body and for the same reason, you can't use a TC on it which is disappointing. It would be great if someone would make a TC for crop cameras and EF-S lenses but it just hasn't happened. But still, without a TX, on a crop camera you have the same field of view and near the same sharpness as a 400mm lens on a 35mm camera. And all for $200 (refurbished). That is simply amazing.
I have a fantastic 70-200 f2.8 EX DG OS HSM that cost me $1200 which rivals the Canon MkI in IQ but with better stabilization and a 1.4x TC as well. And yet when marching band comes up this fall, when we're out there in broad daylight and if I'm going to be shooting at f8, I'll be shooting with the 55-250 instead. It really is that good.
I am serious....and don't call me Shirley.
Canon 7D and a bunch of other stuff