Cant speak for this product but personally ive had great results with ProMa PT5 Petrol Treatment. I kept a spreadhseet for 2 years to track my fuel usage and you could see a notable decrease in economy when you forgot to add it to the tank.
Best economy ive ever gotton though was a custom tune for my Legacy (open road figures)
7.6-8.4 L per 100 km previously 10-11L per 100 km prior to tuning.
Bearing in mind this was after also after installing a bigger dumpipe and decatting and running an extra pound of boost.
PBMS is a great company.