I have successfully setup up my GL-SF1200 and internet works fine on it.
I would now like to setup a Guest Wifi with the download speed limited to 3mbps and the upload speed limited to 512kbps. (I was quite surprised this was not a built-in option as this is a common feature which many routers now have). How do I configure OpenWRT to activate and configure the above features?
(It would be great if the guest network could do MAC filtering, with one common whitelist - is that feature supported?)
What is the firmware version. Have you friend connect to the guest network. Once connected go to the GL.iNet Admin Panel and select clients. In Firmware V4.x select action and add you values. it is in KB 1MB =1000KB
Firmware 4.x :Clients - GL.iNet Docs
Firmware 3.x :Clients - GL.iNet Docs
I do not work for and I am not directly associated with GL.iNet 
Thank you for your input. I use the latest stable version of the firmware which is ver. 3.215 for GL-SF1200.
I do not wish to do individual device wise bandwidth management (i.e. through set static device IP or MAC) but Interface wise bandwidth management so that anyone who connects to the guest wifi is automatically individually limited to the set download and upload limit. (I remember reading that OpenWRT supports such features but I didn’t want to install any new module without being sure it won’t make the system unstable in any manner.)
SQM will do that. Need to download the packages and setup in LuCi NOT the GL.iNet UI thou.
SQM - the OpenWRT page mentions that it is CPU intensive. So is that fine with GL-SF1200. And is it safe to install modules that may not have been tested by GL.iNet itself on the router?
Need to download the packages and setup in LuCi NOT the GL.iNet UI thou.
Could you clarify this - I am not familiar with OpenWRT and so didn’t fully understand what you mean?
What is the speed on private wifi?
There should be no difference between private and guest wifi in speed.
I have a 100 Mbps connection. I wish to setup 3 wifi network - 2g, 5g and guest. I use 5g for my personal use and 2g for friends (both these don’t need any bandwidth limit). I use the guest Wifi network to connect all my smart home and Alexa device and so want to limit their speed to 2048 kbps / 512 kbps and ensure they don’t have access to my other devices on the WLAN.
I am not sure if the smart home IOT devices will need to limit speed.
But now you need to limit speed by device mac address on SF1200.
That’s a pity. So is it not recommended to use SQM on GL-SF1200?
This model does not comes with newer openwrt that could run SQM.
Ok, I guess I’ll have to wait for an update and use device based bandwidth limiting for now. Thanks for all the advice and clarifications.