Hi, I use Fix It! Grammar along with the IEW Writing units and we have found that together the two make a great English curriculum. I don’t feel the need to supplement anything else in with them.
The Fix It! focuses on sentence diagramming, vocab, etc. Students are editing a story that is already written, and so they do learn proper paragraph format and also good writing habits through that process.
Like I mentioned we also use their IEW Writing program in conjunction with it. That’s just my opinion of course!
If you haven’t used IEW writing products yet, I suggest starting with their student writing intensive unit for whatever grades your kids are at now. You can choose the appropriate Fix It! Grammar book as well depending on their age. There is a pathway on the IEW website that shows a sample of what to use and when.
Hope that helps!