A second hand Leaf Aptus 22 is still on top of my list for entry level MFDB for my tech camera.
The riskiest aspect of this back seems to be "long" exposures. The information you find on the net about these old backs is usually people that have all sorts of strange problems when these backs were new, probably caused by buggy firmware or early hardware issues which has been fixed later. I've been unable to find out what the status of long exposure of an up to date Aptus 22 back is though.
Using it outdoors at f/11 early morning and evenings there will often be multi-second exposures. If the official number of max 30 seconds is virtually indistinguishable from 1/100, I'm ok although the ISO25 makes it tight. If 1 - 2 stops of DR is lost due to thermal noise I'm not ok.
I do know that CCDs need efficient active cooling to work really well for long exposures, like astro cameras have, and MFDBs don't have that. So I don't have huge expectations, but at some point it becomes too poor for my use case. I want to make sure the Aptus 22 can reach the decency level.
There are usually two aspects of long exposure noise, background thermal noise that reduces overall DR, and hot pixels. I'm not worried about hot pixels as long as they are not too many or too clustered. Strong reduction of DR due to thermal noise is my worry. MFDBs is often praised for their high DR, but when reading about long exposures the term "software noise reduction" and discussions along the lines that "DR is not really that important after all" comes up a bit too often. I don't know if software is used just to remove hot pixels or if it is to mask thermal noise, which of course won't bring back lost DR. I know that great DR can only be had at lowest ISO, which is ok, but if it also requires sub-second shutter speeds I'm in trouble.
It's also a bit unclear about the dark frame, is it auto-made and auto-subtracted from the raw file or not?
If the Aptus 22 is poor, is Aptus 75 any better? Someone recommended to me an Aptus 75 above the 22 without saying why, not sure if it was resolution or if the 22 actually does suck at multi-second exposures and the 75 is significantly better. I know Phase One P25+ is great, and it does seem like the P25 despite limited may actually be significantly better than Aptus 22, but it is hard to find clear answers, and as usual RAW files cannot be found...