I love my Thermapen and use it all the time.
Reasons why I think it is better than the cheaper ones, the reading is extremely fast. I can insert the probe slowly into the meat and see the temperature profile of the meat as it goes in. It works great on this pieces of meat where other thermometers do not.
I always use it to tell when meat I am cooking is done. Works great when I warm up stuff in the microwave too to ensure things are warm to the middle.
This is one item I would definitely purchase again if I could go back and do it all over again.
XL Big Green Egg, Weber Performer Platinum, WSM 22.5"