For those of you who are new to the brand, Nemosine Pens are made in Taiwan, fitted with German-made stainless steel nibs, then assembled, inspected and packaged in the United States. They are a great value buy for an entry-level fountain pen and arrive with everything to get you started, including (6) ink cartridges and a converter for bottled ink filling. As opposed to most brands that only offer 1 or 2 nib sizes for their fountain pens, Nemosine has up to (7) different nib sizes available, including three calligraphic stub nib sizes.
The Singularity is the base model - a resin bodied pen that is light and average-sized. It has a screw on cap that posts well to the back end of the pen while writing. The stainless steel nib writes smoothly, even with the 0.6mm or 0.8mm calligraphic nibs that are available (mine is the 0.6mm). The Singularity is available in an array of colors, including a clear demonstrator model that seems to be the most popular of the line.
The Fission is the heavy artillery - a weighty, metal-bodied pen that has length and girth to go nib-to-nib against a Pelikan M800. Sure, you're not going to get as amazing of writing quality as you would with a Souveran pen, but for $24.95, it is certainly worth the price of admission. The cap screw posts on the backend of the pen, securely extending the length of the pen to a whopping 6.75" with cap posted. The German-made, stainless steel nib is the same that is installed on the Singularity, so you could swap the nibs between the two pen models.
The Neutrino is the new kid on the block and provides a happy medium between the size of the Singularity and the weighted feel of the Fission. The tapered barrel and cap are pleasing to the eye and comfortable for either a man or woman's hand. The nib is smaller than that of the Fission or Singularity, but is still offered in multiple tip sizes (Medium, Fine, Extra-Fine & 1.1mm Calligraphy Stub).
So, now the question becomes, "which Nemosine will be the first that I will own?"