The last time I tried, it was pretty slow to fire up, especially when I tried to run multiple submissions at once. It's also even more overkill for my use case; I currently use isolate (https://github.com/ioi/isolate) which is just a wrapper around cgroups/namespaces, and it's been a lot faster.

Sidenote: I'm not really looking to replace it, I was just asking out of curiosity since this is my first time hearing of unikernels