I only ended up going in to shelter from a heavy storm as I was passing - and I'm not sure you can really call this an 'exhibition'. All you basically do is sit and watch a few videos and then they try the 'hard sell' to try and get you to sign up for some courses and buy the Dianetics book, which I later found you can get online much cheaper. I found them quite forceful to try and get my personal information - presumably to sign me up to their mailing list - and "I'm really not interested" seems not to be in their vocabulary.
It's a strange building (I believe it used to belong to an oil company), it seemed very quiet and almost deserted for a builing of it size, and the few people I did see had fake looking forced smiles and almost "out of it" as if they'd been smoking something strange. It's no wonder Scientology gets called a cult.
By they way, I'm not sure why they call themselves a "major new religion" when I saw nothing even remotely religious by normal standards about the building, or in the contents of the videos they showed me - and it seems they aren't recognised as one in the UK either. They claim millions of members - but I can't have seen more than 5 people that day.