Hi,
In fact there are cases where U-Boot is not functional or conditionally functional so it seems brickable. For example this forum post.
On the other hand if you are right on firmware switch (between OpenWrt/Stock in this case) doesn’t affect GL-iNet’s U-Boot software, it is a good idea to update U-Boot software first, prior to move further.
Anyway, let’s wait for a shadow line router owner with similar stock2openwrt2stock experience, not to risk brand new router.
Thank you.
Safak Kayhan