Hi there Pink, yes I have used it once. Here is my experience, all test showed some kind of line up until 9 dpo. Wondfo dropped off fast though. It stopped being reliably just six days after trigger. Don't know why. First Signal from Walmart was hit and miss the hold time with smu being the best but 7 days after trigger couldn't trust it.
Your test are holding strong to be cheapies. While 6dpo isn't the most common day for implantation it can happen. I forget if you did IUI or IVF...or was it just an ovulation induced cycle? Praying your lines get darker and not lighter so there is no doubt!! Waiting out trigger lines can be so stressful. Make sure you remember to drink plenty of water! Its the first thing I stopped doing whenever I get hard stressed over something. HUGS