Last month I put on P-R tires and went on a 300K. I flatted mid ride, got separated from the main pack and struggled the rest of the ride. I considered ditching them, but went on to use them on a 400K, and so far so good. They feel cushy and fast, but not a lot of rubber to protect from glass shards, etc. I don't think Serf's are any better, get Pasela's if your main concern is flat resistance.