Yeah sorry when I said dark line I meant as dark as the control but not darker.
The instructions I got with them say that a positive is the same as or darker than the control line so same colour lines are positive. (got this info from the white paper insert that came in the bag as it's not on the pouches themselves).

So guess I am one of the lucky few that seem to be ok with these ones - well last month anyway!
Maybe use these as a guide as suggested above and then use more expensive ones when the line starts to change?