It's all unsulphered, as far as I can tell. No difference. Blackstrap is just a step in the processing of molasses. Most folks on here seem to be finding "Grandma's" brand.
I've read both "start using it 1 month into flowering" and " use it the entire grow" so?
I'm using it for the first time @1TBS per gallon. Had some plants a month in. They are doing well and the molasses has definitely bulked them up. However, other plants that were 1-3 weeks into flower are really, really showing improvement on bud size/dankiness.