If the flare isn't controlled more than the Tokina, then I don't see why any one would buy it, unless the price is around $150 or so.
Because the name on the side is canon, and it'll likely be bundled in a kit like the 55-250 is now. Also, I doubt that half the people who are the target audience for this lens (i.e. the general public and the people who buy the 55-250) would even know what flare is before they buy it. This isn't something that's targeted at people who would have bought a 10-22.