Fedi sats as message stamps are far inferior to Cashu sats because they are more complex. We speculate that users will prefer to store larger amounts of sats in self-hosted Lightning Network wallets rather than in Fedi. Once users have accumulated enough Cashu sats, they can open a Lightning Network channel.
Discussion
I agree that cashu is better, and a good choice for your use case.
And maybe cashu would be the "standard" payment processor in my super app, for the reasons you stated.
Self-custodial lightning is ideal for the spending wallet. Cashu solves the uncle jim, the offline, and the not enough sats to justify the fees problems.