We went for the short package and we still got 9 minutes worth of dvd and that is more than enough to be honest. Some of the dvd is 2d but about 6 of the 9 minutes are 4d.
I don't think a couple of extra minutes of filming would justify the difference in price.
Some of it needs to be done in 2d, such as checking the measurements. Also they use the 2d, see where the baby is and then when they have located the face they switched to 4d.
Although there were 9 minutes of dvd, the scan was much longer than that. They pause the recording when they are recording the measurements and when they are trying to encourage the baby into a different position. I was in the room for at least half an hour.
I can really recommend having it done though, very professional service.