Beyond ip security and Nessus
 

The representative of this company :

http://www.beyondip.com/pages/Support/support.htm

has stated the device of this company has no impact on any network device during its vulnerabilities scan, though if it is peak time.

Any insight ?

If we want to do comparison between it and Nessus

The device as representative mentioned it is a special dell box compatible with the specific Linux OS designed for this purpose (vulnerabilities scan).

Looking at their literature briefly, they do not actually scan anything at all, they simply analyze traffic and generate some form of baseline. in future, deviations from that baseline would be flagged, or so it seems. this box would apparently sit on a mirror port, just watching data, like snort does, infact, it probably *IS* snort. if, as their literature says, no packets leave the box whatsoever, you cna't actually doa network scan at all, a la nessus, but just watch and look for abnormalities.