you can purchase extra licenses for 50 Euro each (the first license was 100 Euro). The SQUID kit is BasICColor Display 4 s/w and what appears to be a rebranded i1D2 puck. I use the same s/w but w/ a ColorMunki.
I will say that I'm pretty impressed w/ the software but also the *free* Argyll CMS system (and dispcalgui) that can be used w/ most of the pucks we tend to use. Unfortunately, it (Argyll) doesn't write into the hw of the NEC's, only the video sw LUTs
http://hoech.net/dispcalGUI/All instruments supported by Argyll CMS. For display readings, these currently are:
X-Rite ColorMunki **
X-Rite DTP92
X-Rite DTP94
X-Rite/GretagMacbeth Huey
X-Rite/GretagMacbeth i1 Display 1
X-Rite/GretagMacbeth i1 Display 2/LT
X-Rite/GretagMacbeth i1 Monitor *
X-Rite/GretagMacbeth i1 Pro
X-Rite/GretagMacbeth Spectrolino
Datacolor/ColorVision Spyder 2
Datacolor/ColorVision Spyder 3 **
* Argyll CMS >= 1.0.3
** Argyll CMS >= 1.1.0