My use case is mineral photos, as it turns out. And I would be very surprised if the AI had been trained on these. The sad thing is -- mineral photo backgrounds tend to be very simple and smoothly-varying. Should be a slam dunk. Ah well.
A one-shot background remover doesn't give you the opportunity to interact with it and suggest that it got things wrong here and there.
Yes, I tried one of my mineral photos, and the app made several errors that it shouldn't have, as the foreground was clearly distinct from the background.
I don't know if I'm allowed to post a photo link, but here it is: https://imgur.com/a/V9H1pRH .