performance testing/monitoring

hate to break up the peering thread but i'm wondering if anyone has experience/knowledge of Empirix tools? i worked with them back when they were known as midnight networks but they focused on protocol conformance testing at the time (mid-90s). they're "corporate history" has no mention of midnight though. they do seem to have some network simulation tools which i'm also interested in. heck, i think someone might have even asked about that in the last few days so maybe this is a relevant/appropriate topic. will take replies off-list if not.