They are all configured to auto-update. They have a mix of a small number of plugins - mostly high reputation ones.
They sit there and work and require next to zero maintenance.
Yep, they are regular hack targets. The biggest risk is brute force attempts overwhelming the server (until recently, I ran them on a 256MB VPS, because I like suffering, I guess), but with some decent protection there (e.g., fail2ban) it reduces risk significantly.
I would say if your plugin mix is simple and you have auto-updates, there is almost nothing to worry about for the vast majority of people.