I have used them 4 times now. Once I had a problem that DPD didn't turn up the day they were supposed to be, and there was another problem, but it did get sorted, the rest of the time it has been sorted ok.
Yes, the discount is a lot less than 10%, but even with that, they seem one of the few people you can insure musical instruments with if you don't have a hard case and want it insured.