I think one of the biggest challenges today is to get a good measurements of our TX power, almost 100% of the OMs heard reports "my power is about / aprox / near / something between x and y Watts" obviously this excludes those few lucky ones with access to professional instruments. In my knowledge the only "amateur" instrument that reaches up to 2.4GHz is the Daiwa CN-801S-II Meter which costs almost the same of a fully ready to go QO-100 station, and the not less expensive and hard to find Bird slugs. Few months ago I got one of this Chinese digital power meter (picture) that claims go from 1MHz to 5GHz, cheap, but so far can not tell if it is functional.
Measuring power range: -45～-5 dBm (external RF attenuator can be extended to 80dBm)
Measurement resolution: 0.1 dBm power
Measurement frequency range: 1 1MHz-5GHz
Measured power: 1nW ~ 2W
Working voltage: 5V DC (direct selection MICRO-USB powered)
Working current: <50 mA
Working temperature: -40 ° ~ 65 ° degrees Celsius
I just found that injecting a 0dBm @ 2.4GHz from a trustable source it displays -19.0dBm so I suppose I will need to input +19dBm in the correction factor to start, so I placed an external 20.4dB attenuator which brings the correction to +39.4dB.
Using SDR-Console I generated a CW tone on 2.4GHz @ 100% drive and got about 12.5dBm readout (picture), so for me it seems a little exaggerated but it is what is showing. Please let me know if you had made any testing with this type of instrument and the results, also how did you calibrated it?