If he has not changed the scarf slick from what I have seen in the past, I would only get it if I already had a nice regular slick and wanted something to hog material away quickly. It is not for finer work, in my opinion. Ask how much belly it has?
The 2-1/2" seems a little on the narrow side for a slick. My daily use slick is 3-1/4" and is just right, for me. I would also ask if the 3-1/4" fat boy has any belly on it, it should, just a little, with a straight edge applied to back of the blade up next to the edge you should see it touch in the center and a little daylight and each side. But, I suspect it is dead flat, I don't know for sure. From his web page I see the fat boy has a radius on the cutting edge, a necessity.