It's no secret that some of KSP's artwork is not great. Placeholder art made by a number of amateur artists throughout the game's development has resulted in a scattered mess of styles and qualities which is most evident in the part artwork.
We believe that there are a number of places where KSP is missing key parts - for example, where a stack class is missing parts that exist in other classes. Restock+ aims to create parts that fill this niche, and is a wholly optional project.