I have been using D005591 consistently for car hire in Italy (7 times during the past year). It has always given me a massive 40% discount! Where they show the rate in the invoice it comes up as Euro Supervalue, whatever that means.
I do not take out any extra insurance with them as I have an annual insurance with
http://www.insurance4carhire.com/, which covers me for Europe for one year for £49, which is less than I would pay for the extra insurance for one car hire with Avis. They also do worldwide cover.
My son is also insuranced with them and recently had an accident in Italy. insurance4carhire returned the approx. £1,000 Avis had charged him in excess. They even returned his taxi costs to pick up another car.