We used this service on the recommendation of our vendor, who probably didn't know any better and did not test it prior. We tried this twice and each time (taking over 3 days), and the migration did not run smoothly. The problem the first time that all fields were totally mapped incorrectly and messed up the order history. The second time around, the refunds over 3 years were messed up. Due to some software limitations, all refund dates were recorded at the time of migration, and not the actual refund date. The company blamed Shopify API and Shopify said they could not do anything. I would caution any company using this service. It might destroy your entire transaction history. Do not use this service.