The convenience of silver gelatin "tintypes" comes at a great cost visually. If you try the commercial product on glass, you'll probably have to sub the plate to get the emulsion to stick. A silane or albumen solution might work.
As Kerik has related, real wetplate collodion is much fun, but inconvenient, and you have to respect the chemistry. IMO though, it really is unmatched in terms of visual qualities.