Efficiency figures can be gleaned from manufacturer web sites.

Mini splits are a number of ways to install AC and heat pumps, not one way. You are probably thinking of the high wall models alone.

Apart from higher efficiency, noise is one large factor.

"Why would you want to put in a MS when you could use a wall unit?"

The through the wall units are almost exactly the same (and in many cases are exactly the same) as a window unit.

They are still far from quiet, and take up half a window.

Mini-slpits tend to not be as loud, but are still worse than central.

I have heard MS are quiet. Friends central air died. Bad compressor. Old system. He could install window unit for localized relief but new system is in the works. $$ though.

Had a Mitsubishi mini-split installed 2 summers ago. It is quieter running inside than most peoples central a/c.
The outside unit is virtually silent, unless you see the fan turning you would not know it is running even when the compressor is going.

Saw an ad for MS. Said it was 22seer? Was warm this spring. Have seen folks running a/c already.

a lot of super insulated homes are moving to MS instead of full ducted distrubution systems. With super tight and insulated homes, your loads are much lower and air distribution issues along with cold spots are reduced.
MS are a great, quiet, and super efficient way to cool and heat your rooms as long as you do not mind the wall mounted unit. However there are some casette ceiling units available, along with short ducted units to cover a few rooms. Your efficiency rating is reduced due to duct loss though.

I THINK infloor hot water heat would be nice in MN. But I want a/c too. If ur house has central air and it dies, putting in a MS unit is sketchy. It makes sense to replace the central air unit. Usually.

It could be 22 SEER. Duct losses would make it stand even taller compared to ducted systems.