I ended up not getting a rental. With the flooding in NYC last weekend it threw my flights for a loop and we ended up only going in a day early for our overnight before flying out to the Caribbean.

As for Uni last time I used it I added it to my account but tried to use it immediately and I still got nailed for the Hertz toll because the transponder wasn't picked up. It doesn't always take 24 hours according to my reading but it can and in my previous case it did.