@Matt Holmer
They sell units with multiple interior units with one exterior unit and I have seen some of these in Europe but the two I had installed were single interior. The 3/1 unit had a 12K BTU unit. I think the 4/2 had a 24K BTU (it was ~5 years ago) and required an extra drop from the utility company and a new panel.
With one interior unit they work best with open floor plans but neither of my units are very open. For bedrooms to get any significant cooling the doors must be open. For more money you could opt for multiple interior units for better heat/cooling of the bedrooms but at some point the cost will start to approach forced air HVAC.
I think the tenants are mostly happy because they went from no AC to having AC. A big reason I put them in is that the 4/2 had 2 wall type heaters and one had been flagged as dangerous by the local utility company. So I was going to be either repairing or replacing a wall heater regardless. There was no existing ducting due to the heat being via the wall heaters. The wall heaters have the same issue with heating bedrooms (i.e. they heat the bedrooms best if the doors are open).
I think the need for multiple interior units depends on the expectations of tenants. Where most of my units are (Escondido, CA) it is hot but the tenants do not expect air conditioning. I have one unit with a new (1 year old) AC (fairly efficient) that they do not use the AC due to the cost.
The 2 units I am considering installing Splits into now not only do not have any ducting but they have no attic (vaulted ceiling everywhere which adds to the heat issue). They both have a single wall heater for heating. So a central interior split would match what they currently have for heating and would provide them some AC.