it worked ok for us on the front, but on the back I just couldn't get it snug enough to be comfy. it carries quite low, so DD would swing out to the side to see stuff - which meant it pulled on my back even more, and this was exacerbated by the short body of the ergo (so easier to lean out and away from me). The only other full-buckle soft structured carrier I've tried is an olive&applesauce, and that was much better - carried higher and longer body, plus would adjust down a bit more. Still not great, though.
I think sometimes you need a bit of helping jigging it just right - baby needs to be seated well to distribute the weight down on hips - maybe give some thought to where you're wearing the waist band - higher or lower - and shoulder straps need to be very snug.