jmb-
I havnt personally used them, but I have a lot of experience with them...heres why....
My daughter was born via surrogate mother to my husband and I. We had to track our surrogates cycles every month so we knew when the inseminations would be most effective.....
This is a good site for info...
http://www.fertilityfriend.com/
there are instructions on each package of detectors you get...and honestly the cheap ones work just as good as the expensive ones.
Here is a good link to info...
http://www.canfp.org/artman/publish/article_57.shtml