Hi, I'll put my two cents in. I'm the owner of ZenWiFi ET8 and was actually curious about Orbi because ET8 has some major issues and terrible support, I'd say zero support because I didn't receive even a single response since I've bought this thing.
My setup is similar to yours. The main router is connected to the internet and the satellite is in another part of the house connected via the WiFi 6e backhaul and has a NAS attached to it via Ethernet. Everything seemed to be great in the beginning, WiFi speeds above 300Mbps in every room, and roaming worked (though it required some tweaks, especially the smart connect rules!).
I can also say the 6e backhaul is quite good, the speeds are around 2Gbps and it doesn't affect the performance of other bands, which is great. I don't have 6e devices at the moment so bought the ET8 system especially with this in mind, that the 6e band will be used by the backhaul only.
Then I configured Plex on my NAS and here's where things go wrong... Every time any other client in the network is being roamed from the router to satellite, other clients in the network lose connectivity to the NAS, which disrupts the playback. I can reproduce this and have reported it to ASUS (with zero feedback, of course).
So I start playing a movie on my MacBook, which is connected to the main router, grab my iPhone, and move closer to the satellite, the phone is roamed to the satellite but my mac, at the same time, loses connection to the NAS and the playback freezes. I tried running 3 ping commands from my mac to the router, the satellite, and the NAS, once the phone is roamed to the satellite my mac loses connection to both the satellite and the NAS for about 20-30 seconds. But it keeps working on the phone, where I also started a ping command! So there are bugs in the firmware, something is going wrong with the network configuration and roam event breaks the connectivity. While this is happening the router shows the satellite is connected and the connection is great so I guess the bug is somewhere in the network routes in the router.
I've mentioned Plex just as an example, of course, this affects many other parts of the network. For example, my TimeMachine backups on mac often break because the network drive disconnects randomly, connections between other devices in the network break, etc.
Another issue is with the kernel and drivers they use. There are multiple kernel panic errors in the logs, I was able to debug them and found there's a bug in the chip driver they use, I even found people who fixed that with an explanation of what's wrong. Also reported to ASUS, also ignored. As a result, routers may reboot unexpectedly.
Firmware updates are rare and it doesn't feel they worry about all these problems. Netgear was my last hope but it seems they aren't any better. Marketing takes a bigger part of the budget than the development, it seems. Ads are great and promising but in reality, all this garbage simply doesn't work as promised and there is no reliable mesh system on the market at the moment.