I have both as well and I agree with the other statements in this thread.
I use the AK differently than the A4; Especially the poly aspect.
I tend to play more chords with the AK and I also use the live record function a lot more.
With the A4 I mainly used the small keyboard to trigger the sound I was tweaking and to change the key as I was sequencing the trigs.
With the AK I tend to use the live record and actually play the notes and then adjust the trigs’ plocks after that.
Entirely different workflow; I find that I now use the A4 for percussion and bass (single note trigs) and the Ak for strings, pads, and chords.
The screen is rather annoying though, it seems to best used standing above it which isn’t exactly how I work (especially when creating a sound).
If they would of simply angled it rather than have it sit flat it would of made a ton of difference.
I have my A4 in a case that allows me to angle it and I prefer to use it that way. Sadly there is no way to change the angle on the AK.
One more thing; the AK has a rather large empty area on the right hand side of the keyboard. I find myself placing my forearm on said area and leaning over to tweak the knobs (kind of like you would to sleep on a desk at school) I find that I am thankful for this as it seems to be the most comfortable way to dig into the parms.