How can they make this work financially?
They claim to "spin up a node for every channel".
Say every node is on DigitalOcean, where one instance costs ~$11 PER MONTH.
How on earth are they paying for that?
They spin up each node on your device, not on digital ocean. It doesn't cost anything to run software on your phone.
Many lightning wallets run a node on your phone, including breeze, phoenix, and simple bitcoin wallet. Mutiny just runs several. It helps that a full lightning node does not have huge storage and bandwidth requirements like a full bitcoin node does.
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