For our 1st child, we had one as we were both “Older Parents” and wanted the triple test (to check for downs syndrome) which wasn’t available on the NHS at the time.
It was a worrying time, but the scan itself was wonderful. the measurements taken reduced the probability of anything being wrong and the 1 to 1 with the doctor who performed the scan was great and a huge contrast to the standard NHS Scan we had at 20 weeks.
The 20 week scan was just in and out with no dialogue, nothing, very disappointing really for 2 excited parents.
For No2 we paid for another 3D scan locally but not at the hospital.
I`d say do it, it was wonderful to really see our daughter and made the whole thing somehow more “real”