Hi. One is always better per device. This is because in some cases they are of different maneuver. For example, for electronics in general they are of immediate action and also immediate reestablishment when the voltage level is good. For refrigeration in general they have a delay of 3 minutes to be restored. This is due to the fact that the compressors must "eliminate" their last compression cycle so that when they return the energy, they do not "add up" to the previous one and can burn their motor or compressor. Placing one for the whole house means that before an electrical problem you will stay in the dark until it normalizes. If engines have been burned it is due to low voltage. What can be placed is an automatic stabilizer for the whole house but it is expensive many times because of the power it must deliver. regards