I put them in the same category as the stealths........ perhaps the stealth valve job is more consistent.
I always redo that anyway, so that’s not a factor for me.

I have seen some SM valve jobs that really needed some attention, so plan for that if you go that route.

When the SM aren’t on sale, I think the stealths are cheaper.

SM are available as straight or angle plug.

I had some SM here that showed in the specs on line that they were 75cc chambers.
They were not......... they were 84cc.

The intake port openings are somewhat oddly shaped, with the port divider being way wider/thicker than the gasket.