OP: I expect that the transponder can only be "read" when the box is slid to the open position. I doubt that the box is anything more than a device to prevent the transponder from being read in those cases where the renter can:

1. pay the tolls in cash;

2. pay the tolls directly to the toll authority after the fact by going to the toll authority's website; or

3. pay the tolls with his own personal E-Z Pass transponder.

I don't think that MA offers option #2, but they certainly offer option #3. So if you do plan to rent cars with some frequency in the future, I suggest that you get your own E-Z Pass transponder. If you still reside in Western NY as your FT profile indicates, you can probably obtain one at the customer-service counter of your local Wegmans supermarket. (That's where I got mine.)

Do you own a car? If not, and you don't want to pay the daily liability insurance supplement fee when you rent, you might consider pricing a personal, non-owner automobile-liability policy. Mine is issued by Travelers Insurance; you should be able to find a Travelers agent near you.