Etoll is by far and away the reason I am working to minimize the amount in which I use Avis. I essentially only rent cars for business and when tolls trickle in up to 90 days after I incur the charge it becomes a real annoyance to track this. Further, the "off" leaver is complete ........ as I live in FL and routinely bring my own sunpass as that is automatically reimbursed by work, come to find out (90 or more days later) I have been double charged plus their "daily" fee. Try to ask them to take it out, I sure haven't had much luck.
Let me point out National as a counter example. They only hit me if I am registered as having "run" the toll, which to date hasn't happened once.
I've heard that in order to really make sure that eToll doesn't double charge you that you can just place the thing in the microwave for five seconds...