There is no ideal length for all product copies. Instead, they should be as long as required to cover the benefits and features, but short enough so you don’t lose the consumer’s interest. A tip is to use the first few lines to help the user better understand the product. Every sentence should then guide them towards a purchase, not distract the user.
Consider the audience you’re targeting and the type of content length that works best for them. Factors to consider include the preferred device of your ideal consumer, as well as their location and age. If they’re not aware of your product, a longer description is ideal, but if they are aware, a shorter copy simply focused on the benefits will convert better.