I’ve only used them twice (on Sinkansen, and on a regular train in Hokkaido), and it was nearly instantaneous – about as fast as an IC card. The whole experience felt like magic: you put the tichets into a slot,
whoosh! – and you pick them up on the other side.
It is true that they are expensive to produce and hard to recycle, though, so it’s a good idea overall. But I’ll miss this iconic experience (or hopefully they retain it on some lines at least). (Edit: or just make the whoosh! readers work with QR codes! :)