I just bought a Delta Parthenope and thought that I would post a brief review...
Overall, I am a pleased. I find the styling quite reminiscent of vintage pens of the early thirties. In particular, the cap and overall lines of the pen evoke the styling of the (likely mistakenly labelled) transitional Equi-Poised. Combine this with a roller clip and there is enough homage to vintage pen styling to satisfy even me.
Now for the pen itself... The pen has quite large barrel diameter at the section (maybe a bit large for me, but I'm learning to be comfortable with it). Overall, the pen is a bit shorter than one typically finds in moderns - its capped length being only about 5 1/8." Another significant feature is that the barrel end is threaded for secure posting. These two aspects of the design bring me to what is my only cautionary note about this pen. I find that the short length means that it is not comfortable to use the pen without posting the cap (as the barrel end threads hit me right between the thumb and index finger). As the cap must be twisted down to be securely posted, this can be a bit inconvenient for jotting quick notes. Additionally, the threaded barrel end requires a bit of practice in posting so that you don't end up with the pocket clip hitting your hand in a bothersome position. However, if one typically writes for longer stretches at a time, the additional security of have the cap screwed to the barrel end may be a plus. The nib is springy and gives some line variation, and starts right up even after being left uncapped for some time. Overall, I really like the pen and recommend without reservation to those who tend to write for longer stretches.
Dave