Does make a difference
This treatment has been used on my Merrell Moab Ventilator Mid GTX boots, and my wife's Salomon Exit Sport GTX hiking shoes. I bought it specifically because Merrell and Nikwax both recommended this type of treatment for both the Gore-Tex and the mix of leather and fabric. With limited use so far, it has helped to keep water out, and beads on the surface in most cases. I'm sure it also assists in keeping the shoes from holding stains from mud, saps and dirt also, thereby keeping the shoes looking newer for a longer period of time. We have not reached the point where the waterproofing has worn off, therefore can't vouch for its longevity (reason for 4-star rating). Hopefully the Gore-Tex won't leak, but at least this creates another barrier that inhibits water from getting in, and still allows the shoes to breathe properly. So far nothing but good things to say about it. I would purchase this product again, and would recommend it if you have similar footwear, regardless if it has Gore-Tex or not.