They're pretty safe. And they heat during a power outage. If you have babies or toddlers You can put a fence like thing around the floor furnace to protect any babies or toddlers from coming into contact with it.
But other than that floor furnaces are a pretty safe and reliable source of heat.
I grew up in a house with one and the heat coming from the floor furnace was great. I remember my mom even cooking dinner on it once when we had a power outage.