I have this bike(model with out self start) for about 4 years. I had learn to ride on this bike so it took some heavy damage at that time. in spite of that the engine is running very smoothly.
It has problems with gear change particularly with second gear but now I am used to it and now it is smooth in my definition.
It has dum brakes on both the tires and they are not good requires frequent maintenance. I changed front one after about 30000km. I have changed the clutch plate after about 22000 km.
Milage I think one should not decide about bikes on this criteria as milage can be increased or decreased on the basis of road and bike condition and tuning. To clear the idea let me say that if you decrease the oil that is entering the engine through tuning and road condition is like national highway then I have tested that my bike gives 84 km/lit, but this way you will destroy your engine.
On the other hand in lab condition where the bike is suspended in air and where there is no friction (ideal condition) the bike will give 100 or more km/lit.I found that with optimum tuning ( which is good for engine) my bike gives 58 to 60 km/lit in kolkata and 68 to 72 in highway which I think is very good for 125 cc bike.
Light is I think is a bit low for high way (ok for the city though) so I have modified my bikes electrical system now I use higher power head light and 2, 55w fog light and high power horn. (12 v 14 ah battery in place 2.5 ah small battery which I got with the new bike)
I think the greatest disadvantage is that the bike do not have the carrier and you will not get one in the market either, I know that now a days carrier is a bit old fashion but they are very handy in my opinion. (in my bike I made a special carrier of stainless steal from lathe and I faced a lot of difficulties in doing so). The comfort of riding is excellent with this bike and you can go for long ride without any troble.
Bike is very stable even at high speed (110 km/h). The top speed of this bike is 110 km/h and if you ride in this speed it still gives 62 km/lit in highway. This bike is very very reliable if maintained properly (air pressure, engine oil, battery, fuel spark plug should be checked regularly). It is very good bike to buy I feel it even after four year.( most of the new bajaj bikes gets really rusty only after 3 or 3.5 years)