But how / or why is it that the trezor site and the Electrum clients generate diff QR codes for the same address ?
There are different sizes of QR codes, different versions of QR codes, different ways to encode the data, different methods of error correction, different degrees of error correction, etc., meaning the same data can produce different QR codes.
In addition, it is possible to encode more information that just the address in a QR code. One code may also include a request for payment, an amount to be sent, or even additional information which will be read by your wallet (Example: Electrum contains a "description" field which can be encoded in the QR code).
As long as they both scan to the correct address, nothing to worry about.
lol... I didn't even thing of added info. That said, if the electrum QR's include a note field. I may incorporate it's QR codea into my sm peoject instead of those provided by trezor. I'll have to scan each with the coinbase app later to see what's what.
Cost will be approx $13, but a dual sided ID card. One with BTC logo, address typed and address QR. With the reverse being LTC . Size of a credit card, kept in the wallet. If needed to receive coin. Just gotta pull it out.