Okay, so I got the Synology DS214se.
And noticed that I overlooked some nasty detail: its support for file systems other than ext4 is only for external drives, so one is stuck with ext4.
Now, I have read several seemingly knowledgeable people explain that ext4 is quite sensitive to power loss - so badly that it may trash a partition unrecoverably. (I am not quite an expert on file systems or linux, but that scenario was explicitly outlined)
This quite upsets me - since it makes having a darn expensive RAID-1 setup rather pointless, doesn't it? I convinced myself to spend over 400 EUR for some more storage "because data loss gets a lot more unlikely", so now this is kinda disappointing, to put it mildly.
I guess I'm still searching for a NAS then, one that supports a file system which lends itself better to data safety.
Well, have to research that subject more, when I got the time *sigh*