In Phoenix they solve the low value wallet problem with JIT/zero conf. I'm curious how Spark compares to that solution. Phoenixd also handles low sat payments with a custodial credit system so maybe that's the biggest difference. You can receive but not resend low values.
Discussion
Phoenix refuses first-receives under a threshold and generally has relatively high fees due to liquidity allocation and on-chain costs. Graduated wallets allow the LSP to allocate substantially less liquidity and allow the first receive to be as low as a zap. It’s a much better UX if you get all the pieces working.
The phoenixd server handles small first receives differently than mobile app Phoenix. The fee credit system might be interesting as a comparison, with the main caveat that small receives are only accumulated until they can be used to open a channel.
I don’t find the “fee credit” system interesting for a consumer product at all (and I guess ACINQ broadly agrees given they don’t use it in Phoenix). The first payment is *the* experience that a wallet has to get right (and then every other payment but the first one matters a lot). If the first payment is just “thanks for the money, we’re keeping this to pay for fees in the future” I don’t buy that people would keep using that wallet.