DIR-868L with Asuswrt-Merlin firmware update:
Improvements on WiFi connection performance between AiMesh router and node after installed USB cooler on both of them.
1. Before only two bars. Now three bars. This the same so far.

2. Before connection quality rating is Good or OK. Now it is Great. Same here.

3. Physical connection rate improved. Before I was getting 234 - 351 Mbps.
This changes over time. Sometimes 351 Mbps, 468 Mbps and higher. Still an improvement than without any cooling.

So, adding the USB coolers does improve WiFi performance too.
Maybe the 2.4G and 5G radios are operating better because of the cooling.
4. OKLA Speedtest from upstairs PC connected via LAN cable to AiMesh node. Before downloads getting 90 plus Mbps. Now doubled.


This make sense as AiMesh node is still a repeater. DL speed is usually 40-60% of PHY connection rate because of repeater mode. However, UL speed did not reduced by much.
FYI, I am having a 300Mbps DL/50 Mbps DL fiber connection to the modem.
We are using Maxis because my wife likes Astro. Astro is giving a rebate when bundle fiber internet and Astro together.
AiMesh router is connected to the modem. I am getting 290+ Mbps/46+ Mbps from the AiMesh router when tested with OKLA Speedtest on my phone.
5. Recently, I am getting random disconnection from the AiMesh node to the AiMesh router.
My wife told me this when she was using her computer. The node will reconnect again after a few minutes.
There is no problem with the AiMesh router.
I recalled having this problem when using DLink firmware last time at the repeater node too.
I did not recalled having this with the ASUS RT-AC66U B1 firmware.
Maybe I did not noticed because I was running this firmware only for a few weeks before I moved to Asuswrt-Merlin firmware.
Anyone having similar random disconnections from the AiMesh node?
Just wondering whether it is a hardware thing for DLink DIR-868L router to behave this way? It seems that changing the firmware did not resolve the issue.
Other than that, I am quite satisfied with the AiMesh system in my home. Performing better and more stable when compared to DLink's factory firmware.
I think gary_cheah85 is right in saying that Asuswrt-Merlin firmware is quite solid and stable.
So far so good.
Regards,
Updated 14 March 2021
Latest update in Roaming Assistant testing.
Final dB value for my home 2.4 GHz -40 dB and 5 GHz -50 dB.
Speedtest from AiMesh node @ WiFi 5 GHz, second floor, after the revised settings.
Before, I was getting 90+ Mbps, never reached 100 Mbps for downloads.
Now gained about 20 to 30 Mbps more.
Uploads speed already reached maximum possible since cannot get any higher.