This is an interesting discussion. Living in Greece we have 5 split units, of varying ages, but our experience is that we try not to use them as we do not feel comfortable or sleep will with AC. I think this is common throughout Greece. It is less about the costs, which can be high, but rather comfort.
The AC is there for the extreme heat waves we get, usually short for 4 or 5 days, we have the 1st this weekend, predicted to be 40c from Thursday and we will have to use the AC at night, but anything less than that they do not go on.
Perhaps the body biologically acclimatises to the higher temperatures, but we find that during the day and at night leaving the doors open and nets across them is far more comfortable, we get a nice natural airflow through the apartment and it is much more pleasant than AC.
I think it is one of these purchases that seems like a great idea, but the experience in a country where it can be required at times is different in reality. it is 27c in the house right now, with the doors open and that is the temperature we would set the AC at if we needed to put it on.
Personally I would avoid a single compressor with multi-units off it - absolute disaster. We used to have one and the costs of running it are very high. it doesn't matter if you have one unit running, or 5, you have to run this large capacity compressor regardless and that is very expensive. Ours was an LG at the time with 7 heads, it was awful, 300 euro elec bills every month, and the did not change however many heads we ran in the summer.