The model I purchased is a black body with white polka dots (though there were other more sedate options available) which holds five different writing tools. Oh, joy! Choices!
I chose four ink colors in 0.38mm size and the mechanical pencil in 0.5mm. The ink cartridges are avaiable in sizes from 0.28, 0.38, 0.5, 0.7 and 1.0mm. There are 16 different gel color options available for the three smallest diameter pen sizes and just three at the 0.5 and 0.7mm sizes (red, blue and black), which are ballpoint ink. The mechanical pencil is only available in 0.5mm.
To load the pen body, I needed to unscrew the clear tip from the body and then press the ends of the pens into the top until snug. Through the clear tip, I can see the colors and the sizes written on the cartridge bodies. Clicking one of the white levers on the pen halfway will cause the pens to retract for easy transporting.
When organizing the pen and pencil inserts, I put the mechanical pencil on the clip so that it is easy to find. Pushing down on the clip repeatedly advances the lead as you would expect.
The pen body is fairly substantial as a result of holding five tools and completely smooth plastic on the outside which might not be comfortable or conducive for long-form writing. I favor this pen for meeting notes as the different colors allow me to embellish my notes and create call outs with the various colors. I did discover quickly that the ink flow is super smooth and requires the lightest touch to flow which is quite lovely.
In comparison to the Hi-Tec-C ink quality, I would say that the Uni Style Fit ink is silkier and less likely to dry out or jam when left unused. Alternately, the Coleto multi-pen bodies have soft rubber grips to make them more comfortable to hold for long periods of time. My favorite pen body to date in the Lumio 4-color which is very comfortable to hold and not much wider than my Kaweco fountain pens.
Overall, I quite like the Uni Style Fit. Its sturdy for a plastic pen, the inks are smooth and creamy on paper and the colors and sizes available are enough to suit just about any taste. I may try the smaller, 3-color body which might be more comfortable for me to hold though I hate to give up those extra color options.
Uni Style Fit Pen body $3.30, mechanical pen component $3, individual cartridges $1.65 each. Total investment: $12.90.