$5 Xbox Gift Card
helpful for getting low cash amounts
I sometimes don't want a whole 15 bucks, so 5 is quite nice to have as an option so I don't have to use a bunch of cash on one thing I wont use all of for a while.
Don't Forget Taxes
It is easier than using a CC on the system and helps if you don't want a CC tied to your Microsoft account. However, these cards DO NOT include the tax when you purchase an item through the system. If you are buying this to exactly pay for something that is $5, beware because it will turn into $5 + tax (which these cards don't include). Thus whatever you wanted to buy for $5 is not $5 and you'll have to buy another card to pay for it.
After purchase instantly gives code.
I would recommend using a gift card otherwise you have to wait a bit for them to review order for you credit card.