For me the WSM has a much better airflow.
So my experience is that big chunks of meat e.g. a brisket is more even cooked.
I use the Slow‘N‘Sear a lot but to be honest more the sear part of the name. For low and slow it‘s OK for one slab of rib, small pork butt or a meatloaf (e.g. BaconBomb).