301-redirects were commonly used as a method of getting the preferred URL indexed by search engines prior to the canonical tag being introduced. The problem with using 301-redirects is that it loses 'location awareness' in a URL. For example, a product 'laptop' can be in multiple categories, and the folder hierarchy in the URL will be different for the same item depending on the route you use to navigate to it.

Using 301-redirects means that end users, as well as search engines, only get to see a single URL, and therefore lose location awareness through the hierarchy and breadcrumb trail.

Using the canonical tag is better because it allows us to pass location specific information through the URL, giving users a clear idea of where the product lies within the category structure, while at the same time notifying search engines that it is a single page, with a preferred URL.