They are look the same but they are not. I tried to check from the user's feedbacks.
Model 1
These one is the cheapest and have fewer components. Maybe it's the first generation.
Use an inductor 100µH. It has green LED power.
The left button use to turn on/off voltmeter.
The right button use to switch between input and output voltage.
There is a blue PCB version which slightly differences.
Model 2 (MH)
It shows leading zero. Use an inductor 47µH. Both input/output LEDs are red color.
Use only one button for all functions.
Short press = switch between input and output voltage.
1-2 sec = calibration
3 sec = on/off voltmeter
The PCB is bigger than another.
Model 5
Like the model 1, has two buttons but come with more components.
Use an inductor 33µH and input capacitor 100µF.
Both input/output LEDs are red color.
ETC
