The start of the route was a short walk from the Hertford East train station. I was lucky with the weather, it was sunny and warmer than usual for the season.
Many sections following the river (canal) in the northern side of the route are on grass, without an actual path. The route had time to partly dry from the many rain showers we had in the previous weeks but was still muddy in places (and extremely muddy in the section right after Finsbury Park). Despite having parts on road / pavement, especially when getting closer to central London, I would highly recommend using trail shoes to run this route.
The original FKT route no longer works at km2 where it is supposed to cross a railway. The path is permanently blocked for safety reasons (there is a sign from Network Rail about it, a fence and barbed wire). I had to back track, cross the New River, and do a small diversion along the river Lea path (km3/4) which runs parallel, before rejoining the New River at Ware. This diversion should probably become the new FKT route, I noticed the previous FKT record had also followed the river Lea in that area but without commenting on the reason for it.
The route is generally not well marked, but is relatively easy to follow with the gpx and common sense (stick to the canal). Note there are many, many gates along the path, in fact almost every time the path crosses a road (twice: a gate before and a gate after the road). To be fair, it makes the run safer as it forces watching out for cars.
I ran unsupported, carrying a hydration vest, and used 1 litre of a water/electrolyte mix and 4 gels.