What's the switching time of such a circuit?
It sounds good..
Instantaneous, and it is a 'bumpless transfer'. Wire the two diode cathodes leads together and that then wires to the load to be powered. Wire each diode anode lead to it's independent voltage source positive terminal. Both voltage sources must have their negative terminals wired together and then wired to the load's ground return.
Which ever voltage source is +.6 volt higher or more then the other will be the one to normally power the load.