I usually use dollar store tests first, then if I see a faint line that I am pretty sure isn't an evap, I use a FRER. I have gotten my first faint positives between 8-10dpo with the dollar tests. Sometimes with FMU. Sometimes with second morning urine.
This pregnancy I got my first faint positive 10dpo. I was camping that weekend or I would have tested earlier. Lol. I took the dollar test and then the FRER. I accidently used the FRER digi. I was surprised it showed a "yes" with such a faint line on the dollar test.