Re: How safe it is to use 4 letter shortened words?
Their word list and checksum rules differs and if you try to enter a BIP39 seed into Electrum
it may consider it invalid and reject it
Again wrong. Electrum allow importing BIP39 seed phrases. it may consider it invalid and reject it
Maybe the user Ambatman never restored his wallets in Electrum software or he forgot about BIP39 option when importing.
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Note: If the seed words are from another wallet, like the blockchain.info wallet, Bither or Mycelium, then you have to press options and check bip39.
Image source.