They are not unique in providing a bad service. A quick look at these columns will show that no courier company is exempt from bad service.
I was sent a small package, containing one sheet of paper and a (substantial) cheque, from Canada via FedEx Express (next day) delivery. It was sent on 15th November, received yesterday (23rd). When I enquired where it was I was told it was being held for Customs examination. The envelope showed no sign of any Customs interference so I can only assume it was laxity of the part of FedEx that had caused the delay. These courier firms charge an arm and a leg to carry packages I expect better than that.