It's more flexible, and can be used anywhere indoors.
The 3-in-1 sensor is bound to Wyze Thermostat, must be used with the thermostat and is used to control one room or area. It also includes a motion sensor, and is primarily used to monitor home comfort.
Wyze Sense Climate Sensor is less restricted, doesn't require a thermostat, and can be placed in any space to track temperature and humidity. It does not include a motion sensor, and it is used to protect your home in the event of extreme swings in temperature and humidity.