The Instructor Demonstration Kit by Molecular Visions is an affordable lecture size molecular model set. While it is suitable for use in introductory organic chemistry courses, there is some room for improvement. Due to free bond rotation, the model tends to collapse under its own weight and, hence, it is difficult to keep the model in shapes that represent some conformations. Furthermore, the model kit is not very good at representing small rings and multiple bonds. Finally, the set has only a few shorter bonds that accurately represent the length of carbon-hydrogen bonds, which is not enough to represent molecules such as cyclohexane. To address these issues, we supplemented the kit by designing and making additional bonds. In doing so we also expanded the scope of the set to show free electron pairs, partial bonds formed in a transition state and hydrogen bonds.
Comella et al. (Sat,) studied this question.