I had a lot of SKU's (11k) and needed to migrate data from Shopify to Bigcommerce. The original store had a lot of detailed data for the products and a broad range of collections. This work took over a year to do, so redoing it was out of the question. I simply had to migrate all of that work into Bigcommerce. The process took about 8 hours ! but was due to significant complexity in both sites. It was a flawless migration, with all data intact. Excellent outcome, great service!