BlueWallet I think understand. It is custodial. But Muun wallet.... I thought it was non-custodial? Meaning I need to open a channel, i.e. do a on-chain transaction, before receiving fund via lightning?
Muun wallet is open source and self-custodial, and I think they are combining both on-chain transactions and lightning payments in one address.
It's not as simple as other bitcoin wallets and they don't even use only mnemonic code, but they combine something called emergency kit and recovery code.
I think their concept is still early and has some flaws, but I respect they were one of the first wallets to implement Taproot support (maybe because they need it the most).
If you really want to understand Muunwallet better you need to read their documentation and test it for yourself.
Now, BlueWallet is also very user friendly. But they are upfront about being custodial, and also very clear distinction between lightning and onchain.
BlueWallet is very user friendly and easy to use even for beginners, but if you are advanced user you can also use it with your own Lightning Node.
One more advantage is that you can easily connect Blue Wallet with other hardware wallets, and I am not sure this is even possible with Muun wallet.