Blockstream App is a non-custodial and open-source (so they say)
"So they say" is a very appropriate qualification - and not only regarding the open-source claim, but also the claim of being non-custodial. When it comes to holding bitcoin in Lightning Network channels, I would not agree that it is truly non-custodial. At least, Blockstream Green wasn't.
I used Green for Lightning in the past, and at one point I ran into a situation where, after a force-close of a channel, my funds were sent to an address that was not controlled by my seed phrase. Recovering those funds required about five months of back-and-forth with Blockstream support, and most of my messages were simply ignored during that time.
Lightning->Liquid submarine swaps are much safer than direct Lightning channels in Greenlight architecture.