The main drawback to Jim Reid's business is the hazardous nature of diving work. This suggests that there are significant risks and dangers associated with the diving activities that Jim Reid's business undertakes. These hazards could potentially lead to accidents, injuries, or even fatalities, which can have a negative impact on the business's operations, reputation, and overall success. It may also require additional safety measures, training, and insurance costs to mitigate these risks, making it a significant drawback for the business.