They may work in some jurisdictions, but I can tell you that in Alberta, my understanding is that our insurance companies will not insure a home that has only a heat pump. It needs to have a secondary backup, because, as you described, in most places in the province it will routinely get below -30°. If pipes freeze, that causes a major insurance wreck. They're just not practical in the extremely cold climate that we have in Alberta.
On March 28th, 2024. See this statement in context.