I think it may depend on what you are wanting to do. I just purchased a cable, and am looking at the NCS Expert tool to do some programming on the car. I have not tried this yet (haven't even hooked it up), as I just got the cable in this week, but have seen others do it. I think there is a bigger element of risk with it as well. What exactly are you wanting to do with the software? I know the Bavarian Technic stuff is probably a lot easier to use, but it seems like when I looked, they didn't have a lot of coding yet available for the E60 M5. It was more for some data logging, resetting codes, etc. They said that the coding was 'coming' at some point, but there was no time frame given.
Mark