The rigging in Messiah is phenominal and quite easy compared to the Poser setup room.  Messiah has an "Auto Rig" function that is great with minor adjusting for smooth joint manipulation without the tucking of joints that Poser has.

You can load the Poser figures into Messiah for rigging as well as any .obj file.  I haven't tried applying materials to figure objects.

With the rigging, rendering, hair, and soft body functions as a stand-a-lone app is well worth the purchase at $40.00.

Not sure about Poser being a host app with Messiah though.  I haven't been able to find a plugin for poser.  Lightwave, C4D, and other high end apps from what I understand do have a plugin where Messiah rigged figures can be loaded into those apps.

I have just used the Demo version that does not save so can't tell how they work in the apps with plugins. what I have been able to do with Messiah demo has been a joy so far and have become a huge fan.

Looking forward to the goal being reached and receiving my Messiah license to really delve into all it can do.