I haven't raced in that particular series, but I've raced enough at OVRP. It's the best karting facility in the Northeast (I don't count F1Boston 'cuz they only do concession karting, whereas OVRP has true open kart racing, in addition to concession and enduro events like these).
Doing kart enduros is how I've kept my racing skills up while I take a break from the expenses of formula car racing. There's no better bang for the buck. You'll be sore and tired and have some bruises by the end of the day, but you'll love it. I race mostly with EnduranceKarting (endurancekarting.com), definitely the most organized traveling kart enduro series in the Northeast, but I haven't heard anything horrible about the OVRP enduros.
I would look at all three - EnduranceKarting, OVRP and F1Boston, and go to the one with the most convenient location and dates for you. Just do it!!