Thanks. I had the same worry when I was contemplating on this... So what I did was to check online on reviews which was not good most of it, but I also head down to the service center showroom and test it out.
It look ok to me at the showroom even when it's dim at the showroom. So I decided to bit the bullet and buy it. No regrets getting it.
It was the best way for me to get a longer range on a budget... I can't afford the 200-400mm lens or any other longer range.