The most advanced feature...
...of the 1401 was the 1403 chain printer. It was fast, quiet and reliable and produced good clear output. It was still being used in the 1970s on the 360 and 370 series. With it companies could reliably produce cheques and invoices of a consistent quality which could be sent to a customer.
The competing manufacturer I worked for at the time couldn't produce a printer that didn't produce wavy lines until the mid 1970s. Our printers were very fast but didn't produce the quality to send out as commercial documents.
The 1401 processor itself wasn't particularly advanced and was not so different from what was produced by other manufacturers. That came later with the 360 series. But put it together with the excellent card, tape and paper handling capabilities and the 1401 became a winning system.