I have sewn a hundreds of feet of #10 YKK zippers without the use of a zipper foot. And yes a good bit of this was done with the Sailrite Ultrafeed LSZ-1 too.
Save your money, it was a pretty hefty price ($33 each) the last time I looked into it several years ago, the main reason being they are not mass produced. In fact, they make them out of regular feet cut to work like a zipper foot so I suppose you have to pay for that extra labor.
Lastly though, if you are going to do a lot of work with #8''s or especially #5''s you might have no choice as the sewing border is much narrower.
Capt. Bruce Gregory