Someone can easily run a SimpleX relay anonymously, it's no different to Nostr in that sense. It's just the 1 company operating the preset servers in the app, but there's planned to be more in the future, and all of those will be hosted by known companies that signed a legally binding contract to run unmodified server code, and not logging IP addresses except for DDoS prevention. The idea is that anonymous relay operators have no incentive not to store the minimal user data they can access (mainly IP address). You'd want Nostr relays to be run by anonymous operators in an environment where government demand for censorship is high, as relay operators can't be compelled to takedown content if nobody knows who they are. Delivery redundancy is planned (

GitHub

simplex-chat/simplex-chat

SimpleX - the first messaging network operating without user identifiers of any kind - 100% private by design! iOS, Android and desktop apps 📱! ...

Censorship on SimpleX isn't possible in the same way as it is on a public social network, as everything is end-to-end encrypted, so there's not a lot of reason to be actively using multiple relays at the same time for delivering messages, unlike Nostr.