A friend kindly loaned me his West Marine snap tool kit. This isn't Vise Grips, it's a stamped metal plier with one jaw that switches its plastic die between Snap Cap and Snap Bottom. The other jaw is a steel punch that crimps the piece being squeezed, cap or bottom. JUNK! I could never get it to set a snap without distorting it to where it didn't work right. Owner friend told me his experience was about the same. He carries his canvas into an old neighborhood upholstery shop and they set them for him, free. He brings them his business when he needs something made or replaced.
I was installing a new cockpit (storage) cover I bought from Great Lakes Boat Tops. They furnish the snaps but don't set them since they don't know where those on the boat were set. I noticed they have a tool for sale, around $35 or so if I remember. I'd guess it's a decent one.
Me? My cockpit cover project? I got out my little plastic die, the accompanying metal punch, a hammer and a chunk of 4x4 to hammer against. Went at it. I was only installing 24 snaps and it didn't go badly at all. AND!!! They all worked.