Just bumping this one up a little, now the service is running and people have got used to it.
I have noticed that demand on it is increasing (but probably only 4 cars work). Now you see people at Welwyn Garden City that could have got the pervious Kings Cross service picking it out. Maybe because they want the core, or maybe because they are going to the core. Likewise when it gets to the south of the route, you see people letting the Moorgate service go and waiting for the Sevenoaks service.
In the core it is reasonably well loaded. What you can't tell is where people are travelling to / from. I doubt anyone is making the though journey. In fact I would be amazed if people traveling from north of Finsbury Park wanting south of blackfrairs even reach double figures. But it does seem to be attracting users. Be interesting next week when Cross Ral becomes more useful if it gets more demand.
Downside is of course it still is very poor on the reliability from, simply because it has no room if things go wrong. Frequently a slightly late Cambridge - London Kings Cross services delays the Welwyn Garden City - Moorgate which in turn delays the Sevenoaks. Going the Finsbury Park - Alexander Palace part causes delays.
But it does seem to be a welcome addition.