Best FREE GRAMMAR CHECKER APP online closest to GRAMMARLY / Grammarly alternatives

I got an ad for grammarly when I clicked this video im scared

Grammarly is worth it but the possibility of saving £10 a month is always nice

Why use "Grammarly" as the trusted source? Try taking the Grammarly corrected version into another checker to see those results?

So do you think Free grammar checkers should be used?