I like Simply Grammar. I’m using it this year with my 6th grader and used it with his older brother a couple of years ago.
I don’t think it’s “enough.” I wouldn’t stop there. My older son did some diagramming and “Grammar with a Giggle” after Simply Grammar and is doing Our Mother Tongue this year.
I do think there is great benefit in diagramming. For example, have you ever tried to diagram one of Paul’s long sentences in the Bible? Taking the time too look at a phrase and try to figure out where to diagram it makes you think long and hard about the sentence. Moving the phrase on the diagram alter the meaning of the sentence. So, I do insist on learning some diagramming with my kids.