We use ours just for a gross error check when entering the figures. Have to investigate if there is more than 2% difference. Some places where they put tail stands in can cause a bit of a problem with the info on the odd occassion.
We still calculate our own V speeds. I believe that BA uses the speeds that the systems gives them although they must have some way of cross checking it. Not sure. System would have been good in the MK case. Dont know if its fitted on any 200s.