The reason I don’t advise using a hardware wallet like Ledger Nano S for MAID is because most people will probably store other cryptos on the hardware wallet as well. The key selling point of the hardware wallet is that it always keeps the private keys isolated inside. When you start messing about to retrieve your private keys, this sanctity is broken, and you are left with the same security as if you had used a paper wallet, provided that you did your paper wallet generation offline. If you are using the hardware wallet only for MAID, it is a valid option as it at least takes care of the offline generation and storage aspects for you. Just no offline signing without retrieving your private keys until there is Omni support.