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.
Example: https://www.highseer.com/products/pioneer-kwik-e-vac
I think I spent $200 in parts on Amazon and have done 4 heat pumps now. It's a vacuum pump, a scale, and a digital manifold/guage. Punch the numbers for subcool/superheat into a calculator and use the temp probes on the lines where they connect to the condenser and you can even skip the scale.
But then neighbours start complaining about the look of the outdoor units and causing hassle with court orders etc. Really if they want people to move they should make it easy and cheap, so invalidate cosmetic complaints automatically.
