Well suited for Analog Four MK1 with an Elektron Protective Cover PL-2 on. It has the right thickness and height to keep the synth from moving in all but one direction. it is a little wider than the Analog Four so you'll end up with some extra space on the side. But if you fill that pace with the power supply and maybe a couple of other cables it will secure the synth from gliding sideways.
Very nice bag. Good padding, stable and hold its shape well. I feel that my synth is safe and secure in it.
It also have three outer pockets. I like the big one but I don't care much for the two smaller ones and wouldn't use them for stuff that would bother me if they fell out and got lost. The outer pockets are overall not as well padded so stuff there is not as protected as the stuff in the main compartment. Which is fine, they don't need to be and it would probably just be overkill if they were and make the bag bulky.
I am also pleased that it does not smell too much and didn't need to be aired out before using. I remember when I bought the Thomann Producer Backpack and had to hide it in the basement for a year before the smell from it stopped giving me a headache. So I am very happy that this is not the case with this one.