I bought this lens a couple of days ago.
This is not a lens originally intended for astronomy purpose, but instead, it's more like for daily snapshots. It's cheap but with great quality. I have no problem with the plastic mount, the rather simple built quality, as well as the barely usable focusing ring. It's fast and so it's perfect for indoor purpose as well.
Last night, I tried it with my Kenko 2x but it seems like auto-focusing does not work. The lens will try to find the focus point, but it never settles on the correct place. Using it in manual mode work, however. The focal ratio was not detected correctly. This is not the case for my Canon 200mm f2.8L, and so it seems like this lens is not working very peacefully.