The Token really is just a 3rd party permission grant for Auctiva to work (for you) with eBay. It's normal, and I have them for other services I use, like Andale Counters. Once you signup and "pass" that Token, things do happen, so be prepared......
I'd recommend you look through the FAQ section at the HELP link (top of page) to get familiar with some of the most often asked questions. If you like the Scrolling Gallery, free picture hosting, and their nice templates in the One-Page Lister, you probably will like the experience here. I've been using them for well over 2 years. Very nice folks, and they have some plans for more to come.
If you have a store or current listings on ebay, those are pulled when you first start the account with Auctiva. When they are pulled, the Auctiva embeds including the Scrolling Gallery are added, and they will reappear back on ebay after a security check (by ebay). That can take 6+ hours, so plan that switch-over for a good time (like late-evening PST on a weekday). You can also Import Closed listings to short-cut vamping them with Auctiva's Lister for template, etc.
If you're a large store, I'd definitely work-up a cut-over plan and talk with the Auctiva folks and/or post questions in the Forum for advise.
Danno