I have found Fortel the most effective, the one that says you can test before AF is due.
With both my pregnanies I have tested when AF was due or a day late with Crystal and Life Brand (from Chemist) and both times BPN, Fortel came up straight away and not on the 1st morning urine for me.

Interesting to read about the cheaper ones you can get on line. The amount of times I test to make sure I'm right maybe next time I should opt for those!