For such retrieval systems, you would usually use Top-1, Top-5 or Top-something accuracy. Concretely, you have a list of product types (embeddings) in your database (let's say 100 or 100,000 whatever). Then you get your product description, you embed it with your ANN and then you compare it with all product type embs. then you check on which rank the correct product type ends up. From that you can calculate mean rank or top-k accuracy ..