That lens will be good for wildlife/birds, but be aware it will not be good for scenery, portraits, etc.
The only non-canon lens I own is the Tamron 18-270 superzoom, and it stays on my Rebel in my car. I completely disagree about the Canon name - it's not only paying for the name, but the quality and build are better.
The lens you are looking at (or the Tamron or Sigma equivalent) will be nice, but I suspect you'll end up getting a second for those times when you want a wider angle.