Well, it may in fact work, but - you can also buy masks that have been used for decades to protect against asbestos and lead paint dust. They are rated to let through 0.3% of the 0.3 micron particles, which according to a chart on wiki on the subject, is typically the most difficult to filter particle size. Note that Covid travels in droplets and cannot travel as naked virions. They also tend to seal better to your face, and you can buy these masks from Amazon and they are made by 3M.
The drawback of them is you look like you Mean Business wearing them, and it's hard to talk to anyone else. But in terms of protection, this spray is like choosing to wear homemade body armor rather than commercial grade. It may work but it would be stupid to go into a gunfight wearing it if you have a choice of gear actually rated to protect you.