There's a bit of a mix-up of terminology. But I think that I understand now.
When you say HP, you mean one of these right? These are actually called ductless or mini splits.
They come on both AC only models and HP models. The portable units also come in AC only and HP models and AC with electric resistance heat. Those portable units also split between 1 and 2 pipe systems. You'll have to specify which you're talking about.
HP means that the refrigeration component is reversible, allowing heat to be moved either from inside to out (AC) or vise versa(heat). It is significantly more efficient then resistance heat. (Like an conventional electric stove)
1) generally much more noisy then any other type of AC.
2) only 1 speed, on and off. So either it's noisy or it's not cooling. They come with a thermostat built in, so it'll cycle on and off as needed.
3) very low efficiency
- duct pipes must run from unit to outside. Usually with the included window brackets. They don't fit all windows. Some people think they are unsightly, but are still necessary.
- single pipe: sucks air from inside and blows it outside during operation. This is required on these units or else they are just dehumidifiers. This means that the already low efficiency is even lower by wasting the nice conditioned air inside and throwing out outside. (At this point, they are barely better then opening a window, while still using power)
- dual pipe: uses 2 pipes connected to the window bracket. These suck suck air from outside instead to operate. These are more efficient then the single pipe but no where near an installed unit. They are still usually less then 8 SEER.
5) Some countries are still allowing for older r22 systems to be imported. They are half the efficiency as r410 models. It's illegal here.
6) You usually can't tell if a unit is an HP model or AC with resistive heat from the box. Resistive heat is quiet but very expensive to run. Unless you live in a very warm climate and only need heat once a year or less, they cost too much to consider.
7) expect less then 5 years from these. They are cheap and disposable. Nothing to fix on them.
8) They are cheap, and easy to setup. Great for backup, but don't expect long life or great performance from them.
1) more expensive, and must be installed. They are more DIY friendly then conventional ducted "central AC."
2) highest efficiency available of all AC types. Usually between 18-22 SEER and some are higher. At the same cooling level as the portable units, they consume 1 half or 1 third the power. (often less)
3) Whisper quiet. Part of that efficiency, is that they have over 100 capacity levels. It's all controlled by the built in thermostat, so it's still just as easy to use. You generally can't hear the difference in speeds inside, and at the lowest level, it's so quiet it's hard to hear. The Outdoor unit is slightly louder, but still incredibly quiet.
4) expect a solid 5-10 years from these. Some last longer, but they don't make things like they used to.
5) Average price, especially for easy installs. Price difference between AC only and HP models are minor if anything at all these days.
6) There are over a dozen types of indoor unit. The wall version is cheapest and easiest to install, making it even cheaper. (time is money after all) You can get in-wall ducted, in ceiling flush mounted, floor models (they look like covered radiators, etc.
Central AC: (adding for completeness)
1) needs a central ductwork system, not cheap or DIY friendly to install. (most new houses come with it though)
2) a bit less efficient then mini-splits but not by much. (between 14-22 SEER)
3) only the most expensive models are modulating, otherwise you get 1 or 2 capacities. (high, low off) Cheapest units are only on and off, at 14 SEER. The thermal mass of the house offsets this so most people don't notice.
4) They can be just as quiet as the mini splits, but you get what you pay for here. There are methods and add-ons that make them much more quieter and slightly more efficient.
5) Also comes in HP and AC only models. However HP models are generally more expensive. However these are Significantly more configurable.
6) most expensive option and least DIY friendly. Expect a solid 10 years from them, and good performance as long as its cleaned and maintained. (all types of ACs require some maintenance)
If you found someone to install a new mini split for less then 2 grand, that's a great price. (If you don't plan on DIYing this) The install makes or breaks the whole thing. A bad install will cause nothing but headaches. Do since homework on the installer first, and read some of the posts here on how to install one so you know how he's doing.