Heat Pump or Emergency Heat At Low Temps?

I've often wondered if I'd be better off just running my heat pump on emergency heat in really cold weather rather than leaving the outside unit working? Temps here in the past few weeks are so low (teens at night and a few single digits) that the heat runs all night and seems to go in defrost mode 3 or 4 times an hour?



So I'm looking for input from some of the "pros" as to whether emergency heat would be more economical than letting it keep going like it is.



And, if turning on emergency heat is the better option, what outside air temp should that happen at?



Thanks

Heat Pump or Emergency Heat At Low Temps?