I was just looking at this the other day. I haven't compared the two, so a better answer will be from someone who does. But I have used the non-pro version, and I _did_ find the plastic ball-and-socket configuration less than smooth — which is what they're [promoting with the new metal ball-and-socket][1]. So, yeah, the metal construction _is_ the main difference, but I don't think it's insignificant. It's not just a matter of durability, since it's a _functional_ element that's constructed differently.



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<sub>that's the "off-topic now" line :)</sub>

I think the name "Composer" is apt, by the way. It's appropriate for Lensbaby shots where you're working slowing and carefully. The Muse, on the other hand, is much more fluid and fun. It's also considerably cheaper.

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<sub>and that's the "way off-topic" line</sub>

My favorite, though, is the Lensbaby 2.0. The new optic swap system is cool, especially if you're interested in pinhole or [zone plate][2], or if you get really into it and want to change between plastic and glass and so on. But the older models are considerably smaller, and the flexible tubing *more* flexible (and less squeaky, something I find a little bit disturbing with the Muse).


  [1]: http://www.lensbaby.com/forum/read.php?1,147257
  [2]: http://photo.stackexchange.com/questions/11552/what-is-a-zone-plate