Worked well enough for most orders and customers we had to import.
Found that sometimes an error would come back for a row, and all we had to do was re-run the import for that row and it would work. There was nothing actually wrong with the data.
Also, may be more of an issue with Shopify in general and not specifically with Transporter, but receiving errors about 'invalid email address domain' for orders we are trying to import (ie. historical data from our old store) is not helpful. Some addresses were indeed malformed, some likely existed at the time the order was placed but the email server for that domain has since gone down. This kind of check is useful during checkout, but not when we're trying to import old data.
Had some troubles with a couple batches of orders we were trying to import. The import kept failing and did not provide enough information for us to determine why it was failing. The error did not match any described in the troubleshooting documentation provided by Shopify.
Contacted support, who told us that the app is developed by a third party and that our support request would be forwarded to them.
Checked back after a day of not receiving any response from the developer. Shopify support apologized and said they'd reach out to the developer again.
That was 5 days ago, with no communication from the developer whatsoever. In the time since, we broke down our import into smaller batches and ran them one at a time and addressed errors as they came up. That worked, but took an additional couple hours of time for us compared to the rest of the imports we had run.
This app is branded as being built by Shopify, and is only available to Shopify Plus stores. The total lack of response from the developers is not impressive.