How trustworthy are the blue dye tests?

After having some faint positives with Amazon early pregancy tests and some negatives with frep, I thought I would try this Sainsbury's blue dye test. When I took it this morning I thought I could see a faint line, but when I held it up to the light I couldn't. So in a rage, I threw it in the bin. This evening I come back to it. It looks exactly the same. Hint of a faint line but nothing when I held it up to the light, so out of curiosity I thought I'd take the casing off. What I find is indeed a faint line. My question is can it be trusted though? I hear bad things about the blue tests. I'm 11dpo today. Think it's best to stop testing and just wait for AF now.