I'm working at Segment now as a Software Engineer in Infrastructure. We just went through a big effort to remove NSQ (in favor of Kafka). Happy to answer any questions.
Messages are durable (across nodes, not just persisted to the filesystem). Messages are delivered in-order (for a partition). Consumers know all partitions of a topic from startup, it's not eventually consistent.
NSQ has been great honestly, it was just designed with different use cases in mind.