I have SLZB-06M and it offers a router firmware for download (still marked as test release). Haven't tested it, as I use it as coordinator. If you want to play it safe get a SLZB-06 (without the M) or a Zigstar / Tubes Gateway with the CC2652P-Chip, you can flash Z-Stack router firmware from KoenK on those. Zigstar uses the newer revision CC2652P7 in the newer releases of the UZG-01, which does not yet have a router firmware, so avoid those for now if you intend to use them as router (they work great as coordinator though). (source: https://www.facebook.com/groups/HomeAssistant/permalink/3698083280463015/)