I abandoned iPadOS as my main driver last year, but then picked up a mini 6 earlier this year. It was my first experience with iPadOS 15, and I have to be honest--I was wrong to be so pessimistic about multitasking. I feel like they fixed all the main things I've been griping about (lost pairings, multi-window issues, etc.). It came off as a little confusing to me at WWDC, but in every day practice, it was quite easy to pick up, and the best new features are far more discoverable than they have been in the past.
All that is to say I had planned on having the mini 6 as an e-reader, but it does come in handy as a multitasker sometimes too, and I do find the new OS features in that area to be FAR more useful than they have been in the past--so much so that I think even going back to iPadOS 14 would feel primitive in comparison.
Your mileage may vary though--I think the reason I'm having such an easy time with it is that I'm also a daily Mac user and the new multitasking stuff in iPadOS 15 is very Mac-ish in a lot of ways.