Mine went well it lasted 3.5 hours. Forgetting to mention a visa is not a very big deal if you can tell them you had no reason to hide the previous visa refusals. Hiding an information is serious only when they notice that the hidden information would have helped them take a decision which would go against you but if it is not the case you’re good. When I was asked about it I told them clearly that I had no reason to hide such information and it would never affect my credibility and also I would advise you to read and have a very good understanding of your own story as the minister’s representative will be trying to pick up negative points on your story. I did mine without a lawyer because I don’t trust those business people.