I chose the e-brevet option which avoided the need to keep hold of receipts but which perhaps took a little longer at info controls: getting the phone out, waking up the app, tapping, putting the app back to sleep, putting the phone back etc. This is slightly more time consuming than either making a note of the info or (in time honoured Audax fashion), asking another rider or a volunteer at the next control.
Interesting - that's the opposite of my experience. I had my phone easily accessible in my top tube bag, so was able to whip it out, tap in and be on the move again very quickly.
At the Burham info, I arrived to find another rider already there, scratching his head wondering where the fire hydrant was. I had to point it out to him! But within seconds, I was on my way, leaving him to work out which number he needed to write down.
At Sheepcote Lane, I was with another rider when we arrived at the info. Again, I was checked in and on my way while he was still getting his card out and looking for his pen.
At the commercial controls, eg Grain, the e-brevet was definitely time-saving as it meant no need to queue in the shop to get a receipt (I arrived at Grain just after the Islington posse...).
So I'm completely sold on the e-brevet from a rider's perspective. I'll be interested to see what it's like from an organiser's perspective though.
The only minor issue I had was that when I uploaded the GPX to my Garmin, it stripped out the waypoints so painstakingly placed by adamski, so I wasn't always entirely sure where the controls were. For future reference, I'll make sure I have waypoints in place for controls.