Hi, well, there are several differences. Mostro works completely within Nostr, orders are sent to relays and clients show them to users, then all communication between users and mostro, and between users themselves is also through Nostr events.
To use Mostro you don't have to run a mostro instance, that's something extra to decentralize the system.
You can read how it works in more details at: https://mostro.network/docs-english/