I renewed my warranty in October & within a couple of weeks my steering lock packed up, common fault apparently! Car booked in with BMW, fault diagnosed & fixed in 5 hrs. Didn't even have to contact Mondial, just paid BMW the £100 policy excess when I picked up the car.
With regards servicing, I contacted Mondial before renewal & they confirmed any VAT approved garage can carry out the servicing as long as it carried out to BMW service schedule using genuine parts, also beware if you modify your car as this may invalidate the warranty.
Only downside with the policy & I've never heard it mentioned but it's true is that when the car hits 60000 miles the renewal will almost double!