I do think they can be very hit and miss and even if there's a hint of a positive on cheap ones they will say not pregnant, so general advice is to wait until AF due date because of this. I always wait for a fairly decent positive on FRER/cheapie before I use the digital - I'd never use it as my first one - be far too expensive haha!
Eek fingers crossed for you, I got my BFP at 10DPO so you never know! But also still time if you do get a BFN. Good luck!!