Electrum is still using predates BIP39, that's why it's not compatible with the current BIP39.
The 4 letter shortened words will be safe to use because there's no difference. If you generate a new wallet from Electrum, you will not able to retrieve your coins if you use other wallet. If you generate a new wallet from wallet that use BIP39 and you want to retrieve in Electrum, you will have no problem too.
My main concern was that Electrum is using different standard, so when I generated new seed words there WAS some words that could be reconstructed in two ways if saved as 4 letter word.