Meh, outdoor plants have more blemishes. could have been physical or environmental. Was that leaf touching substrate after intial training?
if it's a disease, you'll know soon enough, lol.
all fertilizers are decent. whether they have the right ratio or proper instructions is a maybe, but you can make almost any fertilizer work well. You should not worry about the brand.. jsut what a particular product provides and the ingredients used... brand is irrelevant.