Honestly - I was surprised how usable it was with the stock folded at close targets, not ideal - but,
I fired a 30rd mag from a Mk18 with the stock folded on auto in a mag dump -- it was interesting. Standing you can't really brace the recoil so it goes through arms into body and pushes unlike if you have the stock in.
However seated recoil management was much easier, and I found it easier to engage targets accurately with the stock folded than stock extended into a shoulder when in a moving vehicle.