That's exactly right. I highly recommend you get the option where you get extra value added to the card up front. This is very useful in town for transport that takes Octopus but is not covered by the 3-day free MTR pass, such as ferries, trams, and the Peak Tram. When you leave, you turn in the pass at the airport service desk. They'll give you the $50 deposit back, plus if you added cash value, any unused cash.

After the AE rides and the 3-day free MTR expires, the travel pass becomes just a regular Octopus card, so some people just keep them for use the next time they come to Hong Kong. But, I find that since I buy a new AE travelers pass each time, it's better these days to just turn in your card upon departure.