Pedal Commanders - are these upgrades worth the cost and do they really work or just use more fuel?

A pedal interface and a tune are different things. Pedal interfaces ONLY get rid of the delayed pedal response, or lag, when pressing the gas pedal and very diy. A ecu tune will remap afr, change settings in the ecu and sometimes bcu depending on your tuner and their options. And tunes are done by someone ( usually a professional) with a license to techstream.

The prices of both used to be very similar. But last few years, pedal interfaces have dropped and is worth the money off the pedal experience is all you are looking for.