I haven't used the ketostix - generally because I used to on Atkins and can now tell pretty quickly when in ketosis - but I know a lot of people do( helpful to suss how carb sensitive you are i.e. does eating the bars or water flavouring throw you out..)
Ack. I wouldn't bother. I tried them a few times but they never worked for me.
The fact is that if you do the diet, you'll be in ketosis. Doing the diet and then using the sticks is a bit like doing a pregnancy test all throughout your pregnancy.