The site uses the 301 redirects which are search engine friendly. The 301 redirect tells search engines and browsers that the site has definitely moved. This means that if you share the shortened link on other website, search engines will point to your URL (and not the shortener qrl.la URL).
This is very good for your brand!

Once you set a password, you can assign it to any links that you have purchased and created. Make sure you share the password if you want people to use access the link! You can reuse the same password as many times as you like.
If someone uses a QR code or QRL that is password protected, then they will have to input a password before accessing it. Even though the site will then use a 301 redirect, this will have no impact on search engines due to the password protection.

Please note that QRLs and QR Codes are, by their very nature, used for sharing. Although the link passwords are stored securely, they are also meant to be shared with people who are meant to access link contents. The files and links you upload are not encrypted. If you wish to have greater security of any files you share, then you should encrypt them BEFORE uploading them to this website.

This is a great way to grant access to your products!
If you are a photographer, perhaps you want to share photos with only certain people - your clients. You can upload a zip file with the pictures and password protect the link.
If you are making an offer to a client, you can ensure that only they have access to the PDF.

If you have many customers at the same time, you can upload many files and give each one a different password in order to ensure that each one only sees what they are supposed to.