I built one with vol/blend/tone once. Once. I quickly replaced it with vol/vol/tone. It seemed to me that with the blend in the center I was only getting 50% of each pickup, as opposed to 100% of each, and then having the blend roll back each pickup as it moved from center. Please correct me if I am wrong, but it seemed like the output was greatly reduced. I always liked that concept, but it seems the only way I could get it was with an active system. Maybe it was just my choice of blend pots?