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.