Have been using this lens for a month or so. The only other tele I have used was the canon 70-200f4.
The 70-300 is a very basic lens. For the price that u are paying her, it is a great lens. However, you might have to drop the f-stop by quite a bit to get a reasonably sharp pic. The saturation is a little weak, but this can be easily overcome by doing some basic adjustment in CS.
Once u get the hang of the lens, u will be able to overcome the "slower AF".
So, for 1/2 the price of a 75-300, 1/3 the price of a 70-200f4 or canon 70-300, this lens is definately value for money.