I have a PWA (Web App) created for this website on my home screen. I always check downloaded APKs by uploading them here.
It's smart. It does not always require you to upload the apk. 99% of the time, the APKs from Mobilism are already uploaded and scanned there by other users. In that case, the website simply checked the file hash, skips the upload and shows the scan results.
As for the scan results themselves, I'm not an expert. Maybe others on this thread can help you there.