Kept hearing about the Speed lightning wallet, so I just took the time to look into it. From what I can see :

1. it's custodial lightning,

2. can't find a link to the source code (is it proprietary?),

3. it uses ethereum for USDT (https://www.speed.app/transparency/) "USDT reserve funds are stored in our Ethereum USDT multisig wallets."

Nope.