First Response Early Detection

I'm just wondering how early people tested and received an accurate positive with the early response tests? They are supposed to detect up to 6 days prior to expected AF date, but I'm a bit skeptical and don't want to waste such an expensive test! It's very important for me to find out as early as possible, so I can begin progesterone and prevent another miscarriage, I just don't want to test too early, have a negative, and miss being able to see my doctor right away. Thank you so much for any input!