Canon 100-400 f4.5-5.6 L IS Mark II. vs. Sigma 100-400 5-6.

I was wondering if anybody had any experience with the Sigma f 5.0-6.3 DG OS HSM lens.
How does it compare to the Canon 100-400 f 4.5-5.6 L IS Mark II.
Thanks.

The Sigma is a consumer grade contemporary lens with a consumer grade plastic build, Sigma's lowest line of lenses while the Canon is a professional grade metal build with much higher level of optical glass. The two really aren't competitors with each other in my opinion. So then the question becomes, is it good enough and is the price and weight savings worth the compromises that had to be taken to produce the Sigma. It's probably to early to tell on that front.

Thank you E.J. I appreciate it.
I try to help my friend to choose the right equipment but it seems to me that the sales person at his favorite camera store has more influence on him.
So he keeps buying Nikon then trading it in for Olympus and then most recently trading it in for Canon.
I needed the opinion of a professional, it might be more convincing so I forwarded your message to him.
However, as Paul Simon wrote so eloquently in one of his songs: " All lies and jest, still a man hears what he wants to hear and disregards the rest."
I'm afraid the sales person will win again. I feel sorry for my friend as he looses tons of money on all of those switching and trading them in.

Ah yes, The Boxer!