I still shoot landscapes with a DSLR and one of the 5 filters I use most is a circular polarizer (CPL) as it helps filter out the scattered rays of light that cause glare on water, windows, wet foliage and the wash out the normal blue tint of the sky.

There's not really much to say about a filter though — is it doing its job? Yes.
Does it do its job well? Yes.
Does it do its job well enough to be worth the purchase price? Absolutely yes — the sale of one or two prints taken with this filter will cover the acquisition cost in profit.
Does it make it easy to take landscape shots that will sell? Dexterity plays a big part in this, but this filter helps limit some sources of glare that can (not always) ruin landscape shots. It also works well in light tents and other situations where you have multiple strong light sources coming from different directions.

Being multi-coated glass, they've been pretty careful to limit how much light this filter reflects and once installed on your lens, it's able to aim and shoot fairly accurately, even if you're still using the Use Green Box (Full Auto Mode) on your camera. This is my 4th CPL filter in different lens diameters; I've never had one so big or so bad that I felt either way strong.