I've been using this on Canon lenses for some time. Over the years, I've tried the cheapest polarizers I could find and slim, expensive German models. The cheap polarizers work, but their thickness means a lighting penalty: you lose at least 2 stops of light, and they introduce vignetting (fall-off at the edge of the frame) and reduce overall image contrast. That's why it's worth paying more for this model, which performs every bit as well as my expensive German slice of glass but at a far more reasonable price.
This filter cuts glare without a great penalty in exposure, and I haven't been able to spot any vignetting. It is very solidly constructed, and I like that the outer metal rim of the filter is notched: that means I can use one finger to dial in the right angle of polarization when using a lens hood.
Overall, I am very impressed -- it's worth spending a little more to get far better performance.