Alex, there are many programs for reading epubs on android. The primary ones that I know of are Moon+, Mantano, FB Reader, Cool Reader, and Aldiko. I've tried them all, and all render epubs fine. Have seen no issues with any of them.
One of the key differences between these readers is how much of the formatting instructions in the css they will pick up. I've found Mantano does this most extensively. Some of the other readers purposely ignore many of the css instructions. Regardless of this, as I said, I have seen no problems with epub rendering with any of these reading programs.
As for running android apps on your PC, here's something you may want to look into:
http://www.bluestacks.com/index.html
Have never used it myself, but I assume once you have it installed, you just load the program APK (android app file). You can find many android APK files via a google search.
Hope this helps. You should ask your beta tester what reading program he was using. Could it have been an obscure one?
--Pat