Just installed the pre-compiled Olipro firmware for fun on a spare VMG1312-B10A. In bridge mode jumbo frames are working well:
$ ping -M do -c 4 -s 1472 1.1.1.1
PING 1.1.1.1 (1.1.1.1) 1472(1500) bytes of data.
1480 bytes from 1.1.1.1: icmp_seq=1 ttl=57 time=10.9 ms
1480 bytes from 1.1.1.1: icmp_seq=2 ttl=57 time=10.5 ms
1480 bytes from 1.1.1.1: icmp_seq=3 ttl=57 time=10.5 ms
1480 bytes from 1.1.1.1: icmp_seq=4 ttl=57 time=10.3 ms
Bump the packet length up to 1473 and as expected:
$ ping -M do -c 4 -s 1473 1.1.1.1
PING 1.1.1.1 (1.1.1.1) 1473(1501) bytes of data.
ping: local error: Message too long, mtu=1500
ping: local error: Message too long, mtu=1500
ping: local error: Message too long, mtu=1500
ping: local error: Message too long, mtu=1500
The Zxyel VMG1312-B10A is also working fine with BT multicast TV, IPTV (again, in bridge/modem mode and then fed into a pfsense box).