Had my Mission SE750 Special Editions on a bookshelf for years. They performed fabulously.
Well; better than I expected might be a better qualification…
They were attached to a Sonos Amp
I also have my speakers up on a bookshelf, surrounded by books. I’m sure it can be particular to the speaker (I have LS50s), but I’ve never disliked the sound or had issues. It helps that my shelves are deep, and high, so I have a couple inches clearance all sides and it doesn’t get too boom-y.
Perhaps i’d have them out on stands, if it was my choice, just because that looks better to me and is more optimal for sound. But I got no problem with this set up and it keeps the kids away.
Neat explicitly advertise the Iotas as suitable for placement on shelves. With their horizontal orientation, I think they look a little ungainly on floor stands.