Does anyone know what would be the advantage of using nostr for this instead of the disposable robot generation that robosats has?
Robot generation is for privacy reasons of the parties in a trade. You should generate a new one for each trade.
Nostr is the infrastructure on which the trades run. Relays should be fungible and thus you have built-in censorship resistance (making it permissionless). I wouldn't consider nostr to be a tool for privacy.
That would be my guess, I didn't look much into Mostro.