I've used them since they first came out (and had a much more generous discount). One snag with the barcodes is that they don't work if you board or alight part way along, so for example, a ticket from Merthyr to Bridgend won't scan at the barriers in Cardiff. Frustrating if you fancy getting a snack or something at central. Also annoying if there's not someone at the ticket barriers by the Spar shop.