1. The only 70-300mm Canon lens is the EF 70-300mm IS USM. It is a very useful EF lens but does not compare to the 70-200mm f2.8 IS, which you'd be able to take pictures at faster shutter speed in the same conditions.
2. $1700 is a bargain for this specific lens.
3. Unless you're serious about photography, or make a living off photography, you would not need this lens.
Since you mentioned "EFS" I'd assume you may be referring to the EF-S 55-250mm IS. In that case, it's a very good lens for $150, and should serve the majority of Canon consumer users well enough.
Lets also not forget that this 70-200mm f2.8 IS weighs 3.28 lbs, versus the 14 ounces of the EF-S 55-250mm IS. Completely different purposes even though they are both telephoto zooms.
Don't forget the better-fed twin of the 70-300mm IS USM, the EF 70-300 f/4-5.6L IS USM. Sort of a compromise of the smaller/lighter 55-250 or 70-300 and the 70-200 f/2.8 beasts.