Yes it is quite safe, but will make little change to energy usage, or actually even make them consume more energy. If you are trying to make sure they don't go out at all, what you want is a battery backup. For 800 watts you can use most any surge suppressor, but all they do is break the circuit with over current. For backup purposes you need a battery bank that store at least 1000 watt hours to run two 400's for an hour. Hoping the power comes back quickly. If a surge suppressor flips off, no more light.
I use one that is both a surge suppressor and a timer. I am not worried about backup power, but if I was leaving for three weeks often enough I would.
Tripp Lite 1500VA 900W UPS Battery Back Up for $170.00 US at Amazon
View attachment 825074