Although I did not use it during year 12, I found Grammarly to be effective in ensuring that you maintain high grammatical accuracy in addition to appropriate sentence structure. Regarding grammatical accuracy in particular, I feel that Grammarly is superior to other software that detects grammatical errors, such as Word. This is especially the case with long and complex sentences, where Word may not detect and inform you that a particular word should be written differently, whereas Grammarly does so successfully. In terms of sentence structure, I noticed that Grammarly focus quite a bit on punctuation, particularly commas, also to a greater extent than Word.
I hope this helps!