Flairball - I asked a similar question months ago and I didn't get a straight answer, either.

I love the stuff for upholstery and baseball caps, but I haven't dared to spray my tank with it. I'm not sure why. I guess I'm just paranoid about my $600 kilt.

I don't believe it would have any effect on pilling. It's only designed to resist water and stains, not wear.

As for Riverkilt's math, you'd have to add a couple hundred cans of Scotchguard to the cost of your SWK to equal a tank.