I have a Nitron on a Gen 1, with piggyback reservoir.
Hyperpro only made emulsion shock for the Gen 1, if I recall well, so I went with the Nitron.
There was certainly an improvement compared to the original shock, but I feel it was mostly due to a more suited spring rate and slightly higher height.
My advise if you go with the Nitron, take a look at their R1 with internal reservoir, or if you choose R2 or R3 consider adding the remote pre-load adjuster.
With the piggy back reservoir it's a pain to adjust directly on the shock with the supplied tool.