Any question answered...

The SL42's are machined. The one I'm looking at isn't anodized on the braking surface, either, as it's second hand and been rubbed off or never been anodized. http://hplusson.com/index.php?/sl42/

The current wheel I have is great but is anodized and does indeed squeal like a bitch!

In which case it is very much down to aesthetics.