If the human dosage is 0.5g/kg then gelatin is probably a way cheaper source of getting 40g-50g glycine daily. Most capsules products probably do not contain 50g glycine in an entire bottle. Also, gelatin has other amino acids like proline, hydroxyproline, phenylalanine, etc that also have antiviral effects.
Glycine can be bought quite cheaply, if you buy it in bulk. Plus, I have yet to meet a person not reacting badly to gelatine. I have never encountered any product that isn't heavily contaminated with endotoxin and other junk.