Are you sure that the model you've linked is ok ? from its instructions manual, chapter#2 I read:
#2. DESCRIPTION OF THE INSTRUMENT
- The measurement range concerning the fundamental frequency is 40 to 70 Hz.
- Voltage/Current: Sinusoidal signal (THD < 0.1%)
- Power: Sinusoidal signal, PF = 1, Frequency 50 Hz, Measuring range 10.00 W...999.9 W

NOTES:
- at 20 km/h you might expect 32-36 Hz
- expected THD is well above 20%
- Power measuring range has a minimum starting from 10W