I have all 4 and the only one with the feather tippzed fuzz is the gray one you have pictured, which is the softest brush of them all.
EDIT: I think I misunderstood your question. As long as those bristles feel just as soft as the top side, I wouldn't be too worried. The gray is pretty soft and I've used harder bristles than that on leather before. I've never used my gray brush though for leather or vinyl because so far I've just wiped with a mf towel instead of going through the trouble of screwing in a different brush.