My first reaction is wow! It is small, battery powered. Comes with an optional battery and probe for $23. After I uploaded I connected both to my frequency generator and found that both respond about the same across the range from 0 Hz to 400 kHz, but the Fnirsi is more susceptible to freaking out from RFI. Not sure if it's the cheap probe or other. Will investigate. Both give you a useful (but not totally accurate) from the rated top end of 200 kHz up to 400 kHz.
I paid $25 for the original DSO 138 (no battery, no probe)
Fnirsi-138 Pro
No battery, no probe $17
Battery no probe was $19
Probe, no battery was $21
FNIRSI-138 Pro I paid $23 with battery, probe.
NOTE: There's a warning not to touch metal with connecting the scope to higher voltage sources.
My experience = Battery time: 4 - 5 hours. Recharge: less than 2 hours
===============================
Paraphrased from their manual: FNIRSI-138PRO is a handheld oscilloscope for people in maintenance, R&D, and education. It has a real-time sampling rate of 2.5MS/sand a 200KHz bandwidth. With full trigger function (single, normal, automatic).
It has a one-button AUTO feature.The display has a resolution of 320*240. Optional built-in 1250 mAh lithium battery with continuous use of about 4 hours.
PRODUCT PARAMETERS
USB C supply voltage: 5-6V
Type-C Lithium battery: 4-9V Capacity / 1250mA/h
Sampling Rate: 2.5MS/s
Bandwidth: 200 kHz
Voltage range: X1:±40V(Vpp:80V) X10:±400V(Vpp:800V)
Trigger method: AUTO/Normal/Single
Coupling: AC/DC
PWM output: 3.3V, Frequency:0~80kHz, Duty cycle:0~100%
Display: 2.4" 320*240Size: 65*60*18mm
Weight: 53g (Without battery) 72g (With battery)
www.fnirsi.cn/
===============================
DSO138 Videos
$25 Color Oscilloscope! The Incredible DSO138 • $25 Color Oscilloscope...
Using The $25 DSO138 Oscilloscope • Using The $25 DSO138 O...