Hard decision really. I love my A4, sold it only to get the mk2 which I love even more. It has become the heart of my setup !
I don’t use Ableton that much to play music, mainly for editing tracks.
But when I used OB with A4 it was working without any problem, indeed.
I know that OB can really be interesting to understand quickly how A4 works. It’s make more sense to identify what a parameter does when you have the curve in front of the eyes, and the UI is really extremely well done IMO. You have almost everything under the eyes.
I’ve used a lot A4 as a soundcard to record separately the 4 tracks + FX + Inputs in Ableton, and it was working great !
Check this track, that shows my love for A4 mk1 :
And @Scot_Solida making sense of OB interface :
This album was made with A4 only :