If u want maintain unifi while still using celcom,  then it will be like last time what u been through during install unifi.  They will pull Fibre from their port until ur living room then ask for extra charges here and there if distance above 15m.

2 unifi installer and 1 celcom guy will come during the setup.  I think the 2 unifi installer is ready to pull the wire if u want to maintain unifi and ask got a new celcom line.
Celcom 10mbps only will shine when I start downloading.  Else normal surfing really can't see any diff

how's the coverage?

Same as UniFi