Yes, it is an excellent program. I have used it a couple times myself.
As for the problem, I believe that when the drive dismount error occurs, it corrupts the format data on the hard drive, making it unreadable. The data on the drive is not actually damaged most times and easily recovered. That's also how you can still get files back you delete with the same program. When you delete a file, Windows doesnt actually "erase" the information. Rather, it takes the tag off the front of it that keeps the hard drove from overwriting on it. As long as it hasn't been overwritten, you can recover it.
Today's tidbit brought to you by the letters G and C, and the number 8.