I've used it quite a bit with good results, an object like that shouldn't be a problem. Depending on the software you used to make the model you might want to try another native format to obj converter if you suspect that the obj itself is somehow broken.
You might already know this but keep in mind that you can make good use of meshes too (mesh editor found in Construct\Tools\Mesh Editor\Mesh Editor.exe), they clip correctly with 3D objects and I've found them much better for certain situations.
Entire scenes can be made out of meshes too, I made this back in early 2010. The boxes are 3D boxes while everything else is meshed. Edit:
And to actually answer the question: as far as I know the 3D object plugin was initially a bit of a makeshift solution and there were plans on replacing the library that was used with a better one. Unfortunately it's been so long that I don't remember whether the new version was ever finished or bundled with Construct releases but I remember it existing.Looking at the SVN
reveals that the use of the library was indeed implemented and released.Zotged2012-09-27 10:55:07