May I suggest you add a unique ID to Sonoff product packaging? It can be MacAddress (supposedly unique), or device ID identified by eWeLink app.
Also, it would be great to have a barcode on the label, too, so that when a Sonoff device is sold in any shops or web stores, the unique id can be logged by the shop and when later there is a warranty claim, they can look up in the sales records the sale date of that device idetified by the unique id.
This would be very important for distributors, resellers.
Thank you in advance for considering this.