> There is install, but even that is not really that significant.

The install itself isn't that hard they come pre-charged with refrigerant. I have installed a few of the air-to air myself and had no issues. All you need is a vacuum pump and proper refrigerant manifold or adapters. Vacuum out the lines for at least an hour to draw out all the air and moisture, close valve and let sit for an hour, if the gauge shows no leak, open the heat pump zone valves and you're in business.

A friend did it and had all the refrigerant leak out after a year but he realized the flared end that came from factory was malformed so he cut and re-flared the end, vacuumed out the system, left it overnight, saw no leak, and had an AC tech do the charge. Was solid after that. A from zero charge requires some knowledge of the systems capacity and a scale to weigh the charge so he hired someone to do it.

Probably not for entire apartment buildings since most of them run on oil or gas burning here. I only saw heat pumps on apartment buildings built after 2020 or the single family homes in the affluent areas.