My experience:
Dual plane homemade -power at low rpms, power drops off at higher rpms
Single plane-power at low end and increases all the way up the rpm range
Both run well but single plane factory sand cast manifold runs noticeably smoother, even at idle.
Once I noticed the smoothness and felt the power and speed I knew I wouldn't be going back to Kjet or the homemade dual plane manifold. Not that I have a choice now anyway.