Here's the thread. I'm no expert on grafting so can't really comment on that guy's poor success rate with red rootstock, but I do know of one grafter in the UK who always uses red rootstock - if the graft fails to take he still has an 'atropurpureum' form plant he can sell.
Mostly we use green for understock, but if we run low we don't think twice about using red. It is usually not as vigorous, but the take seems normal. We do use callusing pipes in the winter and mist in the summer. Whether our take percentage would change without those helps I don't know.
