There are plenty of USB to DB9 serial adapters on the market, unfortunately most of these generic adapters don't play nice with proprietary interface cables. To add to the complication, they can cost almost as much as the proprietary interface cable itself. You spend twice as much as you planned and end up aggravated because it doesn't work as easy as you thought it would.
When we attempted to interface a PC without a DB9 serial port to a Yaesu VX-7R radio, we scoured the internet looking for a cable, but came up with nothing. That is when the idea to build a USB interface was hatched. Using our extensive background in building scientific measurement devices that use USB, we designed a solution that is cheaper and easier to use than anything else on the market.