Chanced it. Like the fool I am.
Confident I'll be able to at least return it to the state I got it in though. Maybe. We'll see. Already created a dispute on aliexpress since it wasn't functioning right at the start.
Currently trying to get a refund for the device and using it as a USB drive with a RPi 2 as the USB bit seems to run separately from the network side of things.
I've unsurprisingly come to the conclusion that it isn't the 90s and I can't cope with 100mbit transfer speeds.
I think a RPi 4 instead will be what I end up going for. Gigabit network and USB 3. May as well just order one now.
Running nicely. Wrote a simple little script to rsync over ssh and copy data back to my home server each night. Starts at 00:30 and runs for 8 hours using the "time limit" parameter on rsync. Had a couple of nights where it has stopped early when there's data left to copy, but I think that's probably the connection dropping out and it not continuing. Does the rest the next night so it's not a disaster.
One thing about the "time limit" option is that it needs to be supported at both ends. I wasn't aware that rsync needed rsync at both ends, hadn't really thought about how it worked tbh. So initially the rsync version on my home server was too old and didn't have the new time limit feature. Had to compile from source, but then that worked fine.
Copy 19GB of data in 8 hours across the Internet to my home server. This RPi4 setup lives at my girlfriends where I'm spending most of my time at the moment.