Basically, I guess, it means that the AS 0 solution shouldn't be used, at least not usually.
It's like everything else. Understand what the tools do and what they don't do, and use them appropriately.
A primary risk for an IXP is the existence of a more-specific of the IX peering LAN prefix, a less-specific wouldn’t matter or inflict damage.
So in the above context an AS 0 ROAs can be useful to improve protection of IXP Peering LANs where the IX operator doesn’t want the fabric to be globally reachable - and one of the IX participants failed to correctly EBGP in/out policies.