Dear kcyjtion!
1. Different panels


2. Different optical modules
The N401P board supports only fixed optical modules.
The N501P supports only pluggable optical modules.
3. They support different subracks.


4. The supported tunable wavelength functions are different.
TNU1N401PT53 supports tunable wavelength optical modules that provide for 80 wavelengths tunable in the C band with 50 GHz channel spacing
TNU2N401PF51 supports tunable wavelength optical modules that provide for 96 wavelengths tunable in the extended C band with 50 GHz channel spacing.
TNU5N501P supports tunable wavelength optical modules that provide for 96 wavelengths tunable in the extended C band with 50 GHz channel spacing.
For more information, see the product documentation.
Thank you!