A several-year old thread on DPReview (here) points out that an on-lens FLW would cut some light to the blue and green pixel sites, causing increased noise. A poster also mentions that only Hoya sells FLWs, and FLWs (as of 2009) have become exceedingly rare in camera stores. (Interesting, because Bryan mentions as an aside that no other camera store except Adorama has Hoya FLWs.) The thread in general recommends photographing in raw and using Photoshop to tint the image.
One poster remarks that Bryan sells a lot of books by recommending cliché tricks that result in photos that look like a whole bunch of other photos already on the web.
Maybe Adorama wants to clear out their remaining inventory of FLWs and is using Bryan to do their marketing ...?