Powder Flask Recommended
Although a powder flask may not be necessary, I would recommend one for several reasons that have to do with muzzle loading safety protocol involving the safe handling of powder on a range where others may be shooting as well as yourself. That protocol generally states that people should not dispense powder from an open container, or leave a container of powder uncovered where cinders from someone's gun could enter it. Yes, there are funnel caps that will fit on a 1 lb. cannister of powder, but they usually don't have a very good spout or a valve to control the powder flow into your powder measure. So in essence, the use of a powder flask helps to promote the safer handling of powder. It also helps to control the flow and placement of powder into the powder measure. If the spout on a powder flask is properly trimmed, it can also be used to quickly measure a desired volume of powder so that a person could skip using the powder measure altogether for that load, but that is a more advanced option.
I've found that small plastic funnels can help me dump powder easier into whatever I am trying to load if I can find one that fits.