It is helpful sometimes, but many times it is annoying. You cannot get a good answer or it is suggesting things incorrectly. There is no way to add to the dictionary if it "thinks" you are wrong. Any terminology outside of an 8th grade education level is not understood.

The biggest deal is on some form-fill-in sites using the later HTML5 code, parts of the form disappear. I just went back to the old spell checker.

I may check it out again in a couple of years. I would NOT pay for a subscription. The beta is not ready for charging any money. There is No Way I would pay. This add-on is very buggy.