I used it a few years ago.
They will (or at least about 3 years ago) give you a single out of hours take off OR landing without much formality.
If you want more than one, then you need to fill up the form, and fax off with your insurance details. There was a charge of appx £25 then, and it covered you for out of hours landings up to the next renewal date of your insurance policy.
You obviously still have to pay the landing fees.
Also you still need to get PPR for each airport. If you don't, you might find yourself trapped inside the airport complex with no way out. In my case,they left a gate open for me, when they knew I was coming.
dp