I bought this solely so that my camera (EOS 40D) could focus at infinity with my telescope (home built dobson 8") and a T-ring. Previously, I could not get the camera close enough to focus at infinity. But with this barlow the focal length is long enough that I can focus the camera.
If I didn't have to use it, I would not, as the optics don't seem great, especially for the price. When viewing near the moon (but not *at* the moon), for example, there is a lot of flaring. Also, in my case I don't particularly want the magnification that comes with the barlow; I just needed to fix my focus.
I thought this would work for my astrophotography. I hooked up the adapter to my Nikon d3100 and coupled it to the Celestron NexStar 130 SLT. Bottom line is that it didn't focus. If you are using the same combination, buy the T-Adapter with the built-in Barlow.
Got this to use with my Celestron C-90. When using during daytime would consistently get an image of the center secondary mirror as dark spot/ghost image on the photos. When using just a straight adapter with no built in Barlow this was not seen at all.