OPSWAT File Security for Chrome browser extension is now open source https://www.opswat.com/blog/file-security-for-chrome-is-now-open-source
Not much different than simply uploading to virustotal or other site like that... But you shouldn't download stuff you don't trust anyway. If you're downloading, that means you're trusting it. And if virustotal says it's bad, either you did a mistake with whom to trust, or it's a false positive. In either case, it all goes back to the beginning when you decided to trust the file. Either you trusted it right and there is no problem (false positive), or you trusted it wrong. So the conclusion is, this extension is useless, you gotta learn what to trust and what not, that's the proper way. And you wouldn't know if it's a false positive or not anyway, cuz if you did, then you'd know not to download the file (if it's not false positive) or you'd know to trust it (if it is a false positive), in both cases not needing virustotal and the likes, which once again means, it's useless
It would be more accurate of you to say, "you shouldn't download and run stuff you don't trust". I download a file, then scan prior to opening, or not opening.
I briefly tried it out and then uninstalled it as it was redundant (I have Eset) and it demands that you allow anonymous usage unless you pay them.