may be some one answered already,
this little device increases the oxygen level in the exhaust pipe to lower the carbon monoxide level in it and giving out less lethal GAS as an output.
It is installed only in 125 yet like Paiggo 125 and Cg 125 Deluxe, bikes like cd 70s, cd 100, SD 110 are already low in emissions so the are considered already complaint to Euro II standards that's why you can see EURO II marking on them as well in new models.
PS. it has nothing to do with the bike performance.