If you use off brands, your fondant will not be pure white but a bit off. If this doesn't matter, no worries. I used to use the cheapest marshmallows, shortening, and powdered (icing) sugar. One time I tried it with the name brands and my fondant was pure white. It was also more elastic. For the off brands, I always have to use about a tablespoon of corn syrup to keep it more elastic.
Also if you let it sit overnight and then knead again, the texture is smoother as it breaks down the sugar better. Do make sure you coat your fondant well with shortening, then double wrap in plastic wrap and then put in a re-closeable baggie.
I only use Crisco shortening as the off brands are NOT as white.