The Dart I did was machined closer tolerance and deck heights right on. Line hone was straight. I did 4 Merlins. All 4 were a mess as far as machine accuracy, 2 of them I had to even line hone. Both are good blocks when finished. I give the edge to the Dart.
The Merlin had dowel locating main caps which I really liked. The Dart didn't have that but had a deeper main cap locater than std BBC.
But remember, I'm picky.