I think it was mentioned before, but I have the B&W non-multi coated and have not noticed any issues with the final images. I use it quite a lot on a 12-24 and have only noticed a few times when the effect was not even. Usually this was due to an improper rotation of the CPL. I would image though at 10mm it may be more noticeable.
Spend money for a good filter, but it does not necessarily have to be the most expensive. I'd just stick to the top brand names.