Yes, a really good day out yesterday.
I also used K's in Bovingdon. I only had the route sheet and e-brevet with me anyway, I'd forgotten what the instructions said about the official control, and K's is (I think) where I went last time I did this ride, in 2018. As already said, they were quick and helpful, so I'd use them again.
The e-brevet was interesting, as a first-time user. You get used to these things I think. I couldn't work out why I got yellow triangles on the first two controls, but in retrospect it was obvious - we were buzzing along on the easier, earlier sections and running a couple of minutes ahead of time. I was still slightly ahead at Bovingdon, so I recorded my time as I finished at the cafe instead of as I arrived. After that, the hilly route sections sorted things out and there was no problem slipping back into the official schedule
However, it announced that I was 3.5 km away when I tried to register the Ayot control. That was nonsense, but Phil told me at the finish that it can happen, and retrying can help. Must have been my phone GPS being slow to keep up I think. My wife sometimes tracks my progress in Google Maps, and I can be recorded there as a fair bit behind where I really am.
If we're doing it the other way next time, I think a rousing chorus of "The runaway train went down the hill" should be mandatory going down the Nickey Line into Hemel Hempstead. I made that my whistling tune for yesterday - seemed appropriate. It was, as ever, quite a pull coming up that hill. I've no idea how they managed to get trains up it. In fact, most of the lines seemed to be uphill yesterday, so I'll look forward to the reversed route
I use whistling tunes because I've always found bellls a bit aggressive on shared-use paths. A merry tune carries a long way, and allows others to gauge your speed of approach before they even turn around. Works for me.