Anyone tried bg44k for low mpg?

my 99 civic 1.4 auto with 87,000 miles has very poor mpg. took it to garage and mech said to fill tank up and run till dry and that way id have accurate mpg reading. for a full tank im getting 120 miles . mech said he would check for leaks and if never found any would try forte additive. however there is no leakage in fuel lines or anywhere and no apparent reason for the low mpg. however now ive been told to try BG44K as this is better than forte and does genuine cleaning to 02 sensors, cat and clears deposits better than forte. i have read reviews which sound good but would like to know if any1 has tried bk and with what result thanks..