Anyone have experience with the Dry Fire Mag?

https://ift.tt/3o8mmyq link. Seems pretty simple but I don’t know if it’s worth the $100.Also seems like one could be made maybe? New to Glock so maybe there’s another option that’s cheaper to keep you from racking the slide during dry fire? via /r/CCW https://ift.tt/2Y3IiA9