Duckstation is THE only accepted emulator and that's not gonna change TODAY at least, as to provide a more leveled playing field. As opposed to console that introduces various loading speed across PS1/PS2 and possibly if it was ever released on PSN digital.
As of right now, it doesn't seem like any of the larger PS1 communities seems to accept it as a platform, so I see very little reason as to why I should consider it at this point. Its not impossible that my stance on the matter could change in the future, but today I would not feel comfortable enough to greenlight it.
I can keep it in mind moving forward and ask around, but I'd prefer to see it find a place on some larger PS1 boards to verify that it holds a place within the PS1 emu scene. They are certainly more knowledgeable than me on the matter im sure, whatever example they set: will more likely result in acceptance here.
My assumption is: because it reads games off an SD-card? How is that gonna emulate disc-read speed for CD based systems? That's a large reason why PSIO is generally not accepted already. So I at first glance would be surprised if mister could ever work for these types of systems with accuracy in mind.
I personally don't see why mister should be added as a platform for disc-based systems. I know its much more highly regarded within the NES community for one, probably with cart based systems generally. But the same I suspect: could not be said for PS1.