Only one small problem with the Itronix 6250: The OS. They will work with Microsoft Windows® 95/98, Windows NT 4.0 (according to Itronix) and if you want anything newer--no drivers.
A lot of the used ones have also been in 24x7 fleet use and the displays may be very dim as a result. They are damn near bulletproof, but they're also terribly obsolete at this point. Running the older OSes may mean you just can't run more modern software. Running a newer ruggedized PC, may mean quite a higher price.