Which characteristic affects the product's diffusion rate by describing how well its benefits can be observed?

The characteristic that describes how well a product's benefits can be observed is known as observability. This concept is crucial in understanding the diffusion of innovation, as products that have observable benefits are likely to be adopted more quickly by consumers. When potential adopters can see how a product works or what advantages it offers, they are more inclined to try it and share their experiences with others. This visibility can create buzz and encourage wider acceptance, often leading to a faster adoption curve.

In contrast, characteristics like relative advantage focus more on the perceived benefits compared to existing products, while trialability pertains to the ability for consumers to test the product before full adoption. Observation could also refer to the awareness of product benefits but does not capture the specific measurement of how visible those benefits are to others in the market. Thus, observability plays a critical role in influencing the rate at which a product spreads through a population, making it the correct choice in this context.