This is where you need to be careful.
According to the Fetch TV people, their attitude is "If you buy a set top box through an internet provider, and you leave that internet provider, then pretty much you have a useless set top box that won't connect to any other internet provider (that provides the Fetch TV service).
Fetch TV did advise that they are looking at ways of people being able to use their Fetch TV Set Top Box between different internet providers that offer the Fetch TV service. This was some time ago, and as far as I'm aware, nothing has happened on this front.
To me, Fetch TV's business model is wrong and self defeating. At least when you buy a Foxtel set top box, you know you're stuck with Foxtel. When you buy a Fetch TV set top box through your internet provider, no-one tells you that you are now locked into that provider for life, and Fetch appear to have themselves locked into contracts with resellers whereby they can't deal direct with the end user, even if the end user is no longer with the original company they bought the box from.
You'll also see Fetch TV television ads, which aids confusion, and in my opinion, offers the Fetch TV service, but never advises that dealing direct with Fetch themselves is not available to people who purchase their box through an internet retailer such as iiNet, DoDo, Adam Internet, Optus etc.
You've been warned.
As it currently stands at 31/1/2019, buy a Fetch Set Top Box through a Fetch enabled internet service provider, and you'll have a dead set top box if you leave that provider. Fetch TV will refuse to deal with you, so you have an expensive door stop.