Has anyone had experience with a Doona seat?

No experience, but I’ve read on various other forums that the chair is very unstable when you have an active toddler. It seems ideal when they’re babies and not really moving much yet, but afterwards it seems there’s a chance they could tip over with the chair on top of them.

I have one myself and find it very practical when they're really little (the first three/four months). They even slept in it quite often here! But once they start moving and rolling around, I find it a bit dangerous because they can easily fall out, in my opinion (I don't dare use it during that period either!). Only when they can sit independently and calmly is it again a nice, relaxing cushion for them where they comfortably sat until their third/fourth year to just hang out or read books.

I got one too. At first, my daughter spent a lot of time lying in it, then there was a long period where she didn’t use it at all. When she was about a year old, she started using it as a “beanbag,” so it can still be used for now.