You don't have to tap off if you're on ETS routes. You don't get charged extra, I've written a script to verify this.I am a regular transit user, but there are two big (for me) things putting me off using Arc. First, you have to pay to get the card and then you have to remember to tap off.
If I didn't have to pay to get the card, I would probably be willing to try it.
Also, the card is $6 but you will likely save a lot of money with fare capping. With an Arc card, you don't have to decide ahead of time if it is cheaper to buy a bus pass or just buy tickets. You will automatically be charged the cheaper option.
Auto-reload is fantastic too. You don't have to do anything, your arc card will just automatically work until your credit card expires.




