I would guess that, in the absence of a charge, that it is free for the time being. It’s probably like the Machine executor option - free for now, but may incur a charge in the future. Why not request the option to use it (via the support methods indicated) and if there is a charge now that is too much for you, don’t use it?
I spotted this feature the other day, and was thinking of downgrading some of my containers to
small, for efficiency
While we’re on this subject, it’s worth noting there’s an inconsistency in the linked docs. It says “non-paid users must request to use this feature by opening a ticket”, but if a community user follows that link, they will see “Ticketed support is only available for customers on paid plans”.