I was reading an article online recently and according to it this government's energy policy would be to conserve natural gas by phasing it out for CNG users and inefficient power plants. One way to do this is to increase prices. As we have already heard rumors of linking CNG with Oil prices would cause its price to increase above 100 rs.
If you install it now you will get daily saving of almost 50%.
But due to govt. policies you can't be sure that for how long will you be able to avail this benefit.