[CryptoPunk]

DAG-only chains are very experimental and have unresolved game theoretic vulnerabilities.

IOTA resolves it for now with a centralized coordinator while Nano seems to just be counting on no one attempting to exploit its vulnerabilities until its developers come up with a solution.

They are not ready for major commercial use and there's no guarantee they ever will be.

If a DAG-only protocol can be shown to be secure, it could be a major breakthrough for distributed ledger scalability.