My Take
The free package is very generous. The exercises, though using repetition to drive home the rules, are engaging and some of the topics are pretty interesting and niche leading to some good conversations and research tangents. The diagnostics work well and there is a huge amount of resources for each level. I like that they've added ELL levels too.
Critique wise, it would be good to have a British English version and a way to disable apps like grammerly.
How I Use It
I use it with Years 7-9, having students take the diagnostics then doing the recommended practice. Students do 40 minutes in school per week and more for homework.