It has been designed to attach to the LEE filter holder via the optional 105mm polariser ring.
On a FF digital camera, the Polariser, when attached to a holder with 2 filter slots, will cover 16 / 17mm without physical vignetting.
As well as polarising the light, the filter has a slight warm colour tone - roughly equivalent to an 81a filter - to accentuate landscape colours.
For images where this warmth is not required, the tone is easily removed using colour temperature adjustment in RAW processing or in photo processing software.
Note: As a polariser has differing effects dependant on viewing angle compared to the sun, using a very wide angle lens with a polariser can give uneven colouration in the sky, as some areas of the sky will be more polarised than others (due to the large angle of view).
This effect will occur with any polariser used in this way, and is not indicative of a faulty product.
Just because you can use a polariser at 16mm, does not mean you always should.