Looking at it from a non-OpenWrt angle for a moment, that offer is bold. Last OEM firmware update from 2017(!), streamboost stopped around that time as well. The OEM firmware is bad and has accumulated quite a number of serious security issues in the mean time. They've really dropped the ball clearing their inventory 'in-time'.
With OpenWrt in mind, this is a decent device - but keep in mind that it's 11 years old by now, ipq806x and 802.11ac, so a tad beyond the times. OpenWrt supports it nicely, but there is no nice and easy OEM recovery (serial console required), it does switch to the other (always OEM-) image slot if OpenWrt doesn't finish booting (which is a mixed blessing, on the one hand it helps recovering, on the other hand you end up with the horrible/ insecure (and misconfigured) OEM firmware until you reflash OpenWrt),but if it finished booting but 'just doesn't work' (e.g. trouble with the network drivers), you'll end up with the soldering iron and serial recovery. The QCA9980 wireless isn't great (it's not quite the newer QCA9984, as in the r7800 or nbg6817), but okay.
With OpenWrt this is still a nice device, but 30 EUR is -IMHO- too much for that in 2026 (even more so for the typical enduser who doesn't know about OpenWrt), you are already in a territory for 802.11ax/ wifi6 devices instead.
Disclaimer: I bought one of these (albeit used) half a decade ago, it's a nice device that's still doing a fine job for me. I would have killed for it in 2015, I did buy it without thinking twice in 2020, but in 2026 I would favour filogic 820/ 830 or ipq807x/ ipq60xx/ ipq50xx - maybe not quite as readily available, but options like these still become available from time to time.
I'm not so much about specs (160 MHz on 5 Ghz barely works for 802.11ac anyways), but about practical reliability. QCA9980 was abandoned by Qualcomm rather quickly, there are only few firmware upgrades, while QCA9984 got significantly more/ longer attention. It works, it's not bad, but there is a significant difference (client compatibility, reliability, firmware restarts, etc.). (For QCA9980, ath10k-ct slightly mitigates the situation).
I have a soft spot for this model—I used to own two of them. But it’s a relic of the past now. It had an annoying quirk: it would squeak under heavy 5GHz Wi-Fi load.
Do you have an idea how to easily record / measure some paramaters because I also have a QCA9984 device and once in a while I ask myself about that...is there practical difference quality wise between these two?
Probably was some algorithm because five were already sold before my annoucement plus the now increased traffic thru openwrt users.....so probably it will still take some years before they sold their whole stock :- )