I have recently subscribed to Maxis Fiber 300 Mbps plan. This is what I know about the given router after some digging around. TL;DR it is a piece of shit.
There is no branding logo on the device, it looks like KAON AR2140. In the label at the bottom of the router, it states that the model is AR2140.
Kaonmedia is a Korean company, and this brand is largely unknown in Malaysia. Its website states that "KAON Broadband CPEs are built on OpenWrt framework and pursues the latest version of OpenWrt.".
I like that it is using OpenWRT, as it is an active open-source project with support for a wide selection of devices. Hack-friendly with many packages that can be selectively installed via Opkg package manager.
It is not known what modification Maxis made to this router.
As stated in the bottom label, the default username is "user" and the password is the last 4 characters of the MAC address. Login at http://192.168.1.254. It has access to very limited features, but enough to configure WiFi, but cannot set DNS server.
The administrator username is "administrator", and the password is the serial number (mine is 16 characters). It gives access to full features, including configuring Maxis Fibre PPPoE credentials and the DNS server.
TM routers are known to have backdoors, I am not sure if this router has any backdoor access.
Once you logged in as administrator, you can check Maxis Fibre PPPoE credentials. The username is something like "A123456@home.maxis.com.my". Password is the part before alias '@', e.g. "A123456". I think you can just call Maxis and ask for it.
5 GHz WiFi slow startup. Certain configuration changes require a reboot for changes to take effect. When the router boots up, 2.4 GHz WiFi comes up very fast. It takes a long time (a few minutes) for 5 GHz WiFi to be available. I find it quite irritating.
Low speed 2.4 GHz WiFi. KAON's specification states that the 2.4 GHz WiFi has a transmission rate of 450 Mbps. My test result is in the range from 120+ Mbps to 130+ Mbps. It never gets close to 300 Mbps. I have called Maxi's customer support, the advice is to connect to 5 GHz WiFi to enjoy the subscribed speed.
Edited on 2023-05-30: There is no issue with GbE (Gigabit Ethernet) ports. I was using cables printed with "CAT 5" but the maximum throughput is only 100 Mbps. Thanks Tom Lou for pointing out my mistake.
This is not related to the router but might be useful to you. Maxis is privatizing its IP. You can request for dynamic public IP assignment. It is chargeable at RM 10/month.
It seems the given router is different from the specifications on the KAON website. I am not sure what kind of customizations Maxis has made to this router. Anyway, I don't expect much from free stuff. The general advice is to buy your own WiFi router and use the given router as a backup.