I have ridden a bunch of them in Italy and France. They are super competitive in Italy, not so much over here. Still more competitive/challenging then the average century ride.
The Philadelphia event is put on by the same people who put on the San Diego one so I assume they will have the same format. The entire event is not timed, only one big climb. They give you a timing chip and at the bottom of the climb they have a mat you roll over that reads your chip, another one on the top of the climb as well.
In order to insure safety they start in waves which kinda sucks but considering the ability level of the riders it makes sense.
The riding around Philly can be excellent. I have ridden the Founders ride before US Pro a few times and it was a blast. It is looking like I will have some work on the east coast that week so I might come out for this as well.
I did the San Diego Granfondo both last year and this year and I must say the organization was terrible. I won't do it again.
I heard stories of them running out of water at various rest stops both years. Last year it was warm (80 F) and from what I heard they ran out of water at the top of the long climb. This year they ran out of water after the rest stop after the climb.
This year they didn't provide a route sheet.
This year they started closing some of the rest stops early and when I got to the finish they had closed the event expo. The meal at the finish was also cold and sparce. They didn't even provide all the swag promised as some of it didn't get through customs on time. Still have yet to receive it over a month after the event.
They also chose terrible roads. While they are roads I regularly train on, the last section is attrocious (ok, tought to say that with Paris-Roubaix coming up, but for tarmac it was bad), lots of pot holes, road chewed up, and railway crossings at approximately 30-45 degrees. If this was in Milan some older rider would organize a protest. I heard there were numberous crashed on this section. Not a sectioin I would send a large group of riders.
I didn't touch it. I hard heard they do this and had stocked up down in Valloire. The funny thing is the water is running off fields full of sheep
I hope the US Gran Fondo people get their act together. In Europe these are huge, super competitive events. The support level is amazing and the feed zones are well stocked (Unless you are super slow). They can be some of the most fun you have had on a bike.