We live in an age of rapid product advancement and innovation and ANT+ is continually setting new standards. However, to ensure backwards compatibility between devices and give you ultimate choice, ANT+ specifies minimum requirements for a particular use case. For example, ANT+ weight scales must transmit basic weight data to be certified as compatible. Your device manufacturer has the option of whether or not to add new advanced data metrics of % hydration, % body fat, muscle mass, etc, and only needs to meet minimum requirements to be certified as compliant and listed on the ANT+ Product Directory. By doing things this way, you continue to get new products that will work with existing ones, and you also benefit by any advanced features that manufacturers chose to incorporate.
So you know exactly what you are getting, we suggest that you consult with the product manufacturer and/or app developer before purchasing to verify which specific ANT+ features they support.