At a quick glance, without an exhaustive analysis, I think it requires some work to be deployable:
- I have a problem with the QR library it uses: something obscure on Sourceforge, last commit 4 years ago. It also likes to put web-executable files around, e.g. here. I would rather see it using something maintained via Composer, e.g. BaconQrCode (haven't looked at available options closely, just pointing out one most used).
- It's not up to our code standards, for example it uses handmade HTML in https://github.com/gesinn-it/QRLite/blob/master/QRLite.functions.php - a big no.