From a technical standpoint it's a tough decision. If you know the position of the missing characters you can recover a damaged private key.
Once a QR gets damaged beyond a certain point it's gone forever......
QR-codes have built-in error correction, which can be increased to allow for more damage, but that comes at the cost of a larger QR-code.
Or it can be abused by adding a logo inside the QR-code.This is a nice read on
recovering an incomplete QR-code.
A QR-code makes it much harder to sign a transaction offline. Most people would just use their regular phone for it, and if it works, that's very convenient. But the paranoid user in me would want to keep the keys online.