Why Grade B Maple Syrup?
Grade B is of a Darker Amber color than Grade A and produces the most flavor as it is Grade A further reduced in the boiling process. Grade B is also made late in the Sugaring Season and is a bit more difficult to collect as the quantity will be more limited than in the earlier season. The entire season is Incredibly short though for all Maple Syrup (only 4-6 Weeks). This yields a deeper and more complex flavor than Grade A and as a result is a lot more expensive than Grade A, but well worth the cost considering you may not use or need as much as Grade A. This is especially useful in baked goods when you want the Maple Flavor to really shine through as Grade A just is not powerful enough. With Grade B it takes around 40 gallons of Maple Sap boiled down to produce just roughly one Gallon of Grade B syrup.
With that said, ALL MAPLE SYRUP is wonderful and I would never turn down any. The only rule is just make sure that the only thing you are getting is Maple Syrup and nothing else. Throw away all of your flavored nonsense syrups.