Power isn't cheap, and inefficient is an understatement. In the heatwave last week in Germany I managed to get ours to cool a tiny bedroom from 30 to maybe 26 degrees Celsius.

Doesn't help that in new construction outer walls are usually very well insulated, and inner walls and floors aren't (by design; 70% of total heating cost is evenly split too), so you're working against your neighbors too. We have some stupidly complex building standards often driven by industry lobbying (which also makes building expensive), but installing a mini split hasn't made it on the list.