Just take all such information with a grain of salt. Buy the minimum amount . The price per unit of a reagent often drops dramatically with an increase in the size of the order. But a reagent that will not be soon used can go bad, and becomes a very expensive venture. Resist the temptation to buy a whopping big bottle.
Some reagents come in grades of purity, with a higher price for the more pure reagent.
But the most expensive grade isn't necessarily better, and may give different results. If the grade hasn't been specified, call the manufacturer and explain what you need. For the latter use, in which any contaminants could inhibit the enzyme activity, the BSA must be much more pure. Keep a record of what you ordered. This will make it easier to reorder.