I've used an inflatable footrest in the exit row on the LAX-SYD flight and it was great. Since it was only the two of us, it wasn't obtrusive and probably less obnoxious than bringing down my rollaboard to put my feet on. No complaints from anyone. I've only ever deployed it when I've been in the exit row.
I actually bought one of those hanging hammock things for my feet to use when not in the exit row but have not actually used it. There's so little room I'm not sure if I could get it strung up and then still put my feet through it.