IP vs RS232 two way feedback?

I noticed that some devices note the same 2 way feedback for both IP and RS232.

For example some Denon receivers note for both IP and serial: Volume, Mute, Power, Input, Mode2011+ Models: Net/USB Song, Streaming, Album Art, Interactive Feedback

So does this mean this type of feedback can all go over serial without Roomie connecting directly to a port on the receiver via IP?

Can multiple Roomie Remote’s control over serial simultaneously without issue? Does one method provide more reliable or faster control than the other?

Any info is greatly appreciated, thanks!