Which differences, advantages and disadvantages gl and openwrt firmware ?
OpenWRT:
- the original
GL firmware:
- based on OpenWRT
What do the gl firmware offer, what not offered by Open WRT ffirmware ?
Well, since the GL firmware is just additions to OpenWRT then its mostly benefits.
You get the GL UI.
You can control your router via the GL API.
You have cloud control.
You have optimized drivers for your device (closed source drivers on QSDK and MTK devices).
You have simpler configuration of Wireguard, OpenVPN with all the correct routing done for you.
Adguard support.
Tor support.
Mobile app for a lot of the settings above, with more being added all the time.
So its a lot of convenience features. You can do something with a few clicks in the GL UI, but in Luci, you need to have knowledge and time to do the same things. Even something like setting up Wireguard, requires you do do a lot of SSH commands, while in the GL UI it’s just a few clicks.
Advanced users can just then tweak any security features they want, but that is easier once you have the basics working already.
Disadvantage:
You are not on the absolute latest OpenWRT version. For QSDK routers that is because of Qualcomm. For the ARxxx models, its just because moving to the new version takes time. Everything must be tested properly and things ported over. Sometimes like with 19.0x, the OpenWRT team makes changes that introduce random crashes. This means the upgrade must be delayed until they fix such issues.
gl.inet: great for networking and linux newbies.
openwrt: great for learning networking and linux.
all the rest is pure commercial speculation 
Someone who treat open source as religion wont accept CLOSED SOURCE UI.
cloud control…
not always a good thing
Disadvantage:
The UI only allows one VPN service (OpenVPN, Wireguard, Tor) at the time, so if you want to use for example Wireguard and OpenVPN at the same time this will be restricted by the UI
This is misleading. The correct statement is that “if you want to run OpenVPN/Wireguard/Tor at the same time, you need to configure that yourself, as the UI does not offer this feature”.