I haven't had a treatment with optical express but I had a terrible experience with them after a free consultation, and learnt my lesson. Nothing is free!
I told this really nice and friendly person who assisted me there that I had financial problems and had to think about the best option. She said that I should pay £200 deposit in order not to lose the possible given surgery date. This was on 2nd June. And she said if I changed my mind in three days they would give the money back. Then I had to cancel the appointment for the surgery and asked for a refund. Today is 30th June and since then I have been trying to get the money back, and still haven't. They keep referring me to the head office, this office that office. It was a complete waste of time.
So, if you get to have a consultation with those guys, I would recommend you not to give any money until you are sure.