"Threadnine" appears to be a legitimate online store. It has received a rating of 3.42 stars from 78 reviews on Sitejabber, indicating that most customers are generally satisfied with their purchases. On Trustpilot, "Threadnine" has an excellent rating of 4.4. However, as with any online purchase, it's always a good idea to do your own research and ensure the site is trustworthy before making a purchase.