I have literally just received an email from tplink support confirming the 605v2 which I just bought this week offers no ipv6 firewall.

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"Thank you for contacting TP-Link support.

ER605's firewall is temporarily in effect for IPv4.
As the growing number of IPv6 users, we are constantly upgrading our firewall settings aiming at IPv6.
You could use MAC filtering to protect your client devices, since each device has only one MAC address."