I've installed many Fujitsu RMLQ mini splits. They are the most efficient units I've seen. Upon a call for cool or heat, they start at a low rpm and the longer they run the faster they go. I think its about a 12 minute run time to go from start to full speed. The theory behind the low speed start is to keep the start amperage way down and this is where the savings come into play. The compressors are run on a DC voltage provided by the Invertor
I installed 2 9,000btu units on a first level of a 2 story home. The owners have OIL fired hot water heat. He did not buy any oil during the 2007-08 winter season. He heated his first floor with these 2 units and used a ceramic heater in each of the 3 bedrooms on the second level.
We did have some 14 degree days here and the heat pumps kept the house at the setting of 70 degrees and were cycling. I'm sure it could have pulled 72 or 74 with ease.
He told me his electric bill only increased 150.00/mo over his normal bill, and said its is far less than what he would have spent on oil.