Long before I bought my Speedmaster heads I checked into all this doubt casting on these heads... Everybody who ran them out of the box seem to have good results.. when I got mine I took them down to a machine shop and they took them apart put them back together.
All aspects were inspected.. spring run rate valve run out everything.. all they did was re lubricate the valve guides as they had sat on a shelf for a long time.. they've worked fine so far this year on my Stroker motor with an expensive bottom end..
I've given them a good thrashing and so far no problems...
I see absolutely no need to cast doubt and that's from someone who has them on their expensive bottom end practically out of the box... My-2..