Jint is pokey, but fast enough for most use cases. I went away from it mostly out of a desire to enforce contracts and static typing. I personally use Exor as a one-shot loader when the game using it starts, so yeah, you'd have to get cute with AppDomains if you're worried about reloading. (Last I checked, Mono didn't really support AppDomains and about 50% of my development is on a Mac, so I didn't really care).