That is unfortunately their policy. Actually it would depend on your line quality your subscribed speed etc.

Also Maxis can easily be configured on to a different port (eg: port 2) of your VDSL router.

VDSL can typically get 40-50Mbps speeds so if say you subscribe Unifi 10Mbps & Maxis 10Mbps it shouldnt be an issue. But stupid maxis dont want to do that.

I have both unifi and maxis (Astro IPTV) at the same time in my condo. The way I did this was to apply direct to them without telling them I had unifi. Then when they came actually they cut my unifi. Then I complain to the installer there and then "how dare you simply cut my unifi without my permission"

Then they patch it back. In the MDF room they configured both maxis, Astro & Unifi VLANs on to the same physical cable (not ideal - if you can drag new line from your MDF room to your unit that is better).

Now i have a setup like this

VDSL LAN 1 -> Linksys Router (for Unifi)
VDSL LAN 2 -> Maxis Technicolour Router (for Maxis & Astro IPTV)
VDSL LAN 4 -> Hypp TV



Of course since Unifi & Maxis are sharing the same copper line I tried testing simultaneous 2 Astro HD channel + Hypp TV HD channel, then my broadband speed suffers...