Asustor were pretty useless when mine stopped working, and had a pretty bad ransomware incident where they did a lot of blaming users for their own buggy software. I won't be buying from them again.
It looks like Deadbolt also hit QNAP and Terramaster.
Sort of. Accessible via Asustor's own software which they'd been promoting to users, which I'm pretty sure had some kind of hole punching / bridge node setup so that you could use it even if you were blocking all inbound connections to your NAS. Obviously if you completely disconnect it from the internet in both directions then you're safe (but also can't get updates etc.)