I have no idea why the cable car is there but my 8-year-old saw it and declared he wanted to go on. It opens at 7 in the morning so it's ideal for early risers - I don't think there was anyone else on it at all when we got there at 07:40!
We got the DLR out which was very easy, and the terminal is only 2 mins from Royal Victoria station. We got 360 degree tickets (discount with the Oyster card) and whooshed off. As other reviewers have noted, it doesn't actually stop at all, you hop on whilst it is moving at low speed.
The staff were all really helpful and it was a fun mini-trip.More