Amul butter is an old trusted and valuable brand in indian market, whether it is ghee, butter, milk or anything. amul has secured a safe belief among the hearts of indian people.
I also only beleive in amul butter and never used any other butter. also in restaurant also, when I had a dinner, I always order separate amul butter for the roties.
you can keep amul butter upto 6-7 months if you placed them in freezer. in refrigerator also 1-2 months keeping is safe and I had experimented a lot. I always bought 100gm package in units around 10-12 and thats cool enough for more than a month.
I had never used other butter than this because the taste and smell is very friendly and familiar and its a human tendency to aspect the originals from his past experience.