Retrofitting in-floor electric heating generally means tearing up the floor first, so that can be expensive unless planning to replace it. Depending on where you live and how much heat you need, you may not be able to actually heat the room with in-floor electric. To achieve the needed amount of BTUs, the floor may become uncomfortably hot. You can certainly make the floor more comfortable with it, though. you can get 10-12 BTU/sq ft with electric. You can achieve a lot more heat transfer with hydronic, but that means a boiler. The oil in the heater will probably be a little more even, but heat is heat, and eventually it will all spread out into the room. Heating the whole floor means more even comfort, and no restrictions on where you can place furniture.