Tried, tested and proved to perform, these are thermometers I use and would recommend. There are cheaper ones out there but they might not last the distance or give you accurate results.
A probe thermometer is essential to all BBQ cooking to ensure your food is at the correct temperature for both excellent taste and texture as wells as being safe to eat. The Thermapen 4 is the best.
For dual probe thermometers you get several choices. I like one with Wifi when I’m working at home as it remembers my home network. For classes the convenience of Bluetooth is great as I don’t need to mess around setting it up on a network.