Ava bracelet

Kristin
Has anyone heard about these or have you used them/know of people that have and if they work? 
From what I can tell it's a <a href="https://play.google.com/store/apps/details?id=com.glow.android">fertility tracker</a> that you wear and records temp all day long and gives you your fertile window!! All info is greatly appreciated! 🤗