How fantastic, what brill parents you have. I had one at 27ish weeks which will be similar to you when you go and it was amazing. They were so thorough, spent the first 10-15 mins doing the 3d/4d bit, and getting the pics etc then did all the measurements and stuff which was on the DVD we got.
It was also at the scan that we did find out that the baby was not growing properly and I really think that if we would not have gone for a 4d scan then the baby would possibly not have survived as 3 weeks later he was born by c-section. Not that I'm trying to scare you as it was absolutely amazing and Tomos looks identical to the images we got.
Enjoy it and don't forget to post some piccies. xxxx