I've used it the past two years and it's decent. I have seen better quality webcasts, but it's a good deal for the price, and as UND85 said, they sometimes partner up with away webcasts and through them in for nothing, where if you didn't have Siouxtra you would be spending another $7/game for those. At times it tough to see the puck, especially the shots further out, but all in all not bad. Much of it depends on your internet speed. Many of my youtube clips are taken right from the webcast, so that could give you an idea.
Here's a video with different clips put together, all from the webcast, 5 meg download speed
On the other hand, this is either a cable or dish feed.