To start with, it's a short series featuring some of the major characters in the original Hellsing manga. The story revolves around with Walter (in his youthful years), Integra's father and the Lieutenant. In does not show much of the plot but it presented the history upon the foundation of Hellsing Organization.
For an overall impression, I found the story incomplete since I only read the manga translation. The art and the characters is really good as it depicts their looks before time. To sum it up, if you got curious of what happened 50 years before (to get satisfied with the story), then read it.
There is not much loss when you skip this one.