I bought the high school writing journal alongside the high school reading journal from Not Consumed. I would still add grammar and vocabulary, but with those four components, I'd grant a full credit. I can't imagine just using this writing journal as an entire ELA credit?
I wouldn't count this as a full English credit either as I have looked through it more (because I also think you need literature and vocab). I am going to count it as a creative writing elective though. With the 120 days of lessons plus 10 days of projects (which I think could easily be expanded to make it more robust) would work for an elective credit. But, yes, I don't think I would use it alone for an English credit for a transcript. At the same time, if I look at my local high school, adding in some personal reading and a few more short stories and you do have an english credit for high school so I think it depends what your state requirements are as to what would count.