Very efficient, absolutely, and quiet, OMG yes. Great for that far bedroom that just does not cool down properly, or that addition that has your new large screen TV, and you want to hear it without having to turn the volume high to hear it over the noise of a room air conditioner.
What is the problem?
Filtration is their Achilles heel. Those thin, cheap, plastic washable air filters purported to be anti-fungal etc. really do not filter much, if anything. Okay, so you may not have a problem with allergies, and pollen and dust do not bother you so much. However, the cost of keeping your mini-split system from clogging up over time may give you some pause.
By their current design, there is really no place to install any kind of high efficiency or at the very least, a filter built to at least keep your unit from building up a layer of dirt on the coil, and especially that long blower wheel that they all use to be super quiet.
So, what’s the problem? Just clean it with a brush! Not so fast, the indoor coils have dirt building up between the radiator like fins and the blower wheel is never easily accessible for cleaning, that brush just is not going to cut it. What to do? Spraying chemical coil cleaner and washing the coil and blower wheel is the proper fix.
Simple, right? The problem is that you cannot use a power washer because you will certainly damage the soft aluminum fins plus that unit is inside of your house! Can you imagine the mess if you ask your brother-in-law to help even if he just uses your garden hose?
The proper way to clean the indoor coil and wheel is to install a specially designed bibb all around the indoor coil that drains into a bucket and carefully cover the electronics. Cover the floor underneath with both a plastic and a cloth tarp, then spray coil cleaner on the equipment and either use a hand pump sprayer or a low-pressure power sprayer to rinse off the dirt and chemicals. All this must be done very carefully to prevent water damage to the floor and hopefully the wall does not get too much overspray from the procedure.
I know it does not sound too complicated, but it is a tedious and time-consuming job that requires careful diligence and hopefully not too much furniture movement.
I still think that mini-split systems are great, but you should take this necessary future service procedure into consideration, among others, as to placement of a mini-split system or possible other alternatives that you may wish to consider.