I love these. I'm sure there are many downsides and I don't think its something I would leave in my pond all the time for the reasons listed above, but imagine your friends oohing and ahing over this. How neat!
There's a lot of videos on you tube installing these and using them. Looks like people put food in them to introduce the fish to them. Some use like a 20 gall aquarium so really big fish swim in there.
Since my bottom is not really level, I'm am considering attaching something from the deck, maybe some stiff wire (?) and resting a bowl on that.