Great info! It also points out that a Thermopen should be accurate to 300+ degrees when calibrated in a 'proper' ice bath. Other thermometers may not have that sort of accuracy span. And that invites the potential for trouble even if you perform your ice bath calibration check properly.
An important thing to note: In food service, their main concern is in the proper maintenance and storage of perishible food stuffs at near freezing temperatures. That makes it completely appropriate to calibrate most thermometers with an ice bath. The target temperatures that the Users are aiming for are typically only 10 or 20 degrees F away from that freezing point.
Unfortunately in brewing usage, our target temperatures are well over 100 F away from that freezing point. Its great to see that Thermopen acknowledges that their product will maintain measurement accuracy over the temperature span we are interested in brewing. For any other thermometer, you would be wise to calibrate to a NIST-certified thermometer in the typical mashing temperature range to assure your working thermometer is reading correctly. The freezing point and boiling point calibration still doesn't work for you if you don't have a Thermopen.