It won't affect you because you use Auctiva and not their lister page. I suppose if Auctiva was down and you went to eBay to list you'd be taken to their new lister form in that case.
It's little disappointing that eBay emailed all our users telling them to go use the new lister page. What eBay should have done is seen that a seller had used eBay's SYI page, but had also posted items through a 3rd party. Then included even a line or two about that in their email. Such as: "If you are using a 3rd party such as Auctiva to list your items you should not be impacted by this change unless you were to come list on eBay's SYI form in which case you'd be directed to the new version of that page."