I received a VMG1312 (-B10D) recently from Zen when moving house (as I'd not had a "free" router from them when I first took a VDSL service). Whilst everything else Zen organised was smooth and efficient, ie/ transfering my service from A to B, and keeping my static IP etc, my experience with the VMG1312 was less so. The main issue is that Zen use a provisioning engine to configure the router, and had set this up with the wrong account for the new property (old account, or temporary one). Whatever I did to configure the router for the correct account, at any restart it would re-provision back to the incorrect settings, leaving a house full of unhappy people with no internet access until the configuration was manually corrected each time. In the end Zen removed the router from the provisioning engine which resolved that particular problem.
Long answer therefore that with a standard setup Zen appear to provision the routers with your login details on this router, so it auto connects.
I also found my Draytek Vigor 130 VDSL2 modem (and subsequently the Draytek 2860 integrated router which I've changed to) connect at about 4Mbps faster than the Zyxel. So personally I'm just keeping the Zyxel for emergencies.
| Zen VDSL2 80:20 (~64:20) | Draytek 2820 + Ubiquiti AP + SureSignal + EE Signal Box + Netgear NAS