Not used the Kevlar ones, but put a set of their sintered ones on last week. Out for first ride today with them at Cwmcarn – did about 7 or 8 hard stops from about 15/20 mph on them in the car park to bed them in, then just went for a ride. Had half worn Sram sintered pads in before this – but wanted to put new ones in when I held the brakes for the first time. Can’t see any different in performance either better or worse. Still got more brake than I’ll ever need (running Sram Guide RS with 160mm rotors front and back on a Boardman Pro Fs).
Obviously I can’t comment on longevity. As long as they last ok I’ll be buying more of these in the future.