Conversion units

In the hope of making the use of conversion-units a little clearer, I attempted to compare the output of a car2pol operation in JS and a mapping between Cartesian and polar coordinates.

here is the scenario:

I am expected with the “conversion-units” Device to get the same result the “through-JS” returns.
But I may have miss understood how conversion units are used.

Any input would be greatly appreciated.

Thanks to @jcelerier (again), I understand the usage of conversion units a little beter.
here is the update score :

the only issue remaining that I see is that rho and theta are inverted. The result gives theta first and rho second in the array.

This actually relates to a conversation on Github :