If it does not prominently advertise that
it has been proven in a
SAE/TMC Type fuel economy test
.. Then there is a 90% chance that
It is a fraud.

The big 18 wheel trucking companies
and the Society of Automotive Engineers
help develop these highly accurate and repeatable ways to find out what works and what is "snake oil"

For example

http://www.ooida.com/Benefits&Services/Discounts/Dipetane/SAE-J1321-Dipetane-Test-Overview.pdf

http://www.pavetrack.com/PAVE/Type%20IV%20Fuel%20Economy%20Report%20for%20Omega-Tec.pdf

http://www.airtab.com/aeroflow.html

http://cleanairfleet.com/uploads/SAE-ClaudeTravis.pdf