Purchased online ticket via their website and worked out well at airport.
However, it would not let me exit at KL Sentral.
What was completely ridiculous was the staff at the exit refused to let me exit until they could sort out the problem, which took over 20min.
Wasn't the only person, about 5 of us stuck. Pretty irate after a long flight and 60min train.
Am sure lots of people have used it successfully.
Suggest you take a GRAB using wifi at airport!