The software is just incredible on that thing. I got one with an Intel CPU and can run Docker on it that way. This replaced my PI where i was previously running a few things for home automation.
You can totally setup a NAS with a pi but IMO it's never gonna be as nice as a Synology NAS and all the trouble you have to go through setting it up.
But I can't shake the feeling that they will turn to the dark side sooner or later - the fact that the software is closed, mostly. Definitely if they get acquired, but also all the nice features are begging to be abused once the MBAs see they can get another $1/year/customer from selling you out.
So far, I only have excellent things to say about Synology. The feeling is from past experience with other vendors - Synology themselves have been amazing.
You pay a little extra up-front but it really is worth it. The box also uses a special BTRFS implementation that is rock solid and easy to manage snapshots for with their own GUI tools.