TTC July/August but have irregular cycles

Ok, so I bought an ovacue saliva sensor because my cycles range from 28-36 days and I think this will help pinpoint ov. Better. Has anyone else used this? Can it pinpoint ov or is it just an estimate?

 I truly know nothing of these, are you using opk's and temping as well?  That with what you're planning should give you a good idea.  What are you trying for?