I have not used it and personally don't see the point of it. According to Eric Warner's Classic Beer Style book on Kölsch, brewers in Cologne use pilsner malt and a little wheat to brew their Kölsch. Doing a quick internet search, it appears that the malt you've found (Global Malt Kölsch Malt, I assume) is a slightly darker Pilsner malt made in Cologne (4.5° L as opposed to 2° L with a normal Pils). Beersmith suggests that if you made a Kölsch with 100% Kölsch malt, it would be just a hair too dark (5.8 SRM, while the BJCP suggests an upper limit of 5). Personally, if I wanted to add a little depth to my Kölsch I would just add 10-15% Munich malt, and that seems consistent with what one brewer said over at the morebeer forum: "I've used it once just to try it. It reminds me of when I use a touch of Munich in a kolsch. A little darker color maybe a touch more malty backbone. It is kilned a little higher than pilsner. Since I keep pils on stock and brew kolsch regularly it is not worth it to me to use it more often."