Grammarian is part of the startup on my computer 10.4.11 Used every day all the time. No problems, no slowdowns, no adverse issues other than occasionally a duplication of menu in some programmes, with no impact on functionality.
Highly recommended for people who are serious about the quality of their writing. Best Wishes to the developer who continues to support this valuable software. I would be more than happy to purchase the next version upgrade. I am also a licensed user of Spell Catcher but I find Grammarian to be far superior.