Yes. Grammarly is a reliable plagiarism checker. In fact, Grammarly recently collaborated with ProQuest (an extensive content database) and can now run both onlinand offline checks. What's more Grammarly has some rad add-on features apart from just plagiarism 👇Does Grammarly pick all grammar errors?
Grammarly will not catch all grammatical or writing errors, but it is in my opinion one of the top products currently available on the market. It won't perfect your grammar and writing, however, based on the English in your post it would be worth the investment.