Renault Megane (1.4, P Reg) Immobaliser?

About two weeks ago the immobaliser in my renault died on me and I had to get toad home. Reading forums ive found many people with the same problem, and not willing to pay the full £500 to Renault to fix it. Got a new fob ordered, but the garage is having trouble matching the key and code together.
Now, ive found a site that sells immobaliser disarmers, and was just wondering if anyone has used one, and how it works?

Cheers