I would go with the cheaper brand -- assuming that you liked it as much as Cheerios -- nothing is as expensive as tossed food.
Oat flour is merely oats that are ground finely -- one can make one's own in a food processor. They have the same nutritional value as oats and I believe would be the equivalent in this list of ingredients.
Oat flour isn't tricky like wheat flour because it isn't degermed and debraned (or whatever) to create it in the same way that wheat flour is completely different than whole wheat flour.
I doesn't matter in this context since both are using "oat flour" -- i.e. finely ground oats in the recipe. If one is using principles of Volumetrics of WW Core plan diet, then it does matter as grinding the oats increases the nutritional density -- read calories since the same "amount" of oats takes up a smaller amount of space and is generally not diluted in the same way that whole oats are.
Some days I pray for Silence, Some days I pray for Soul,
Some days I just pray to the God of Sex and Drums and Rock 'N' Roll.