Hi,
New Flint 2 today here and new as well with openwrt (I had a router with ddwrt like 10 years ago). As the title say... how worth is to install the vanilla openwrt? As far I saw, the luci interface seems to be the openwrt or at least a light version? and I can install packages as well, but dont know if it still being the full openwrt and missing other things that you can have with full version.
Thanks.
If you are happy with the current possibilities of your router … no need for plain OpenWrt because the GL GUI won't be available there.
Your router runs OpenWrt already - a special „fork“ made by GL.
If the glinet gui works then stick with it. Easy to use wireguard / openvpn and app control make the glinet gui fork far easier to manage and as you say, under the hood there is Luci so it's basically a nice gui on top with easier navigation.
This depends what direction you wanna go 
If you want a simple router the default firmware is more than suitable.
If you want to go a little advanced often that can also be done (basicly it is just OpenWrt with the freedom to luci to some extend).
But once you go really really advanced, then i'd recommend going with OpenWrt themselves, at this point you will find yourself having so many conflicting issues, or you try to 'hack' around it's not worth it.
^ it can also be you are just interested about performance and wanna see how the latest openwrt 24 snapshot performs without the gl ui counter part.
In my topology i use two flint 2, the main flint 2 is using openwrt with around 10 to 12 vlan networks, with multi psk meaning each wpa2 password has its own vlan, currently im also compiling my own images with patches to help fixing bugs, basicly i went for a lab network design.
my second Flint 2 uses gl firmware with the mtk sdk as i want to use my ayaneo and don't want to destroy my wireless or since today my full network😆
There is many ways really you can go with.
What I found is I cannot configure the DNS properly through the GLGUI as it is too simple, can I configure ControlD profiles depending on the device through commands in the dhcp file with the GL fork?
In the case I flash with vanilla openwrt is there turn back to GL firmware?
Also, I saw the snapshot is updating frequently, but that doenst mean there are always updates right? I cannot find a changelog for version 24
Not through the gl ui, but if you have access to the CLI via ssh you could try install their package, then you can point 127.0.0.1 as your custom dns in the gl ui, OpenWrt unfortunately also have no official package unlike nextdns.
Yes that is possible, however i want to make sure you are aware of the distinction in firmware.
GL-iNet currently has two versions the normal version which uses the mediatek sdk which completely closed with private drivers from mediatek, and the op24 variant which uses openwrt from the master branch (very experimental) and uses mt76.
From MTK sdk to openwrt24 or vice versa due to these wireless incompatibilities and also the difference in partition styles you need U-boot otherwise you brick the router these firmware are too different.
From op24 from gl-inet to openwrt, this is possible, but always use the one with sysupgrade in the name and not factory, the factory replaces u-boot with their own less friendly recovery system.
Either way for both situations you never should check the checkbox keep settings on the upgrade, its wiser to create a backup open this with 7zip and slowly migrate configurations to /etc/config via winscp.
U-boot is basicly your bios, it helps to recover from when a firmware went bad and bricked the router.
Heres the documentation for u-boot:
You can just upgrade the normal way, as long as you don't keep settings. Uboot is not needed.
Still i won't encourage it, better safe than sorry 