First of all yamaha fz25 has the BS-4 engine.
As we know that govt. Of India banned BS-3 vehicles to control pollution caused by vehicles and apply new standards called BS-4.
Then yamaha fz25 is completly valid and can be buy without any govt. Difficulty.
If we talk about the featurs of the bike then in 200-250 cc segment, yamaha fz25 is the best in class because it has more powerful engine of 249 cc, company claimed milage of 43 km/ltr and custemor review milage is about 35-38 km/ltr which is again best in class, its price is much lower as compare to other 250 cc bikes like ktm duke 250 and with the compliments bike is very muscular fuel tank, head light is very aggressive while tale light looks sporty, the bigest feature of the bike is FI system which increase the quality of the bike and take it to the next level.
So if you are planning to buy a beast with its best then without any doubt go to yamaha fz25.