It's not a
big deal. But there is a difference. The basal takes your temp to the hundredth degree. And there is a deffinite difference between .11 and .19 ya know? I bought mine at cvs for 10 dollars so they aren't expensive. I would suggest it though.
I wanted to add that monday through friday it's easy because I take it as soon as my dh's alarm goes off. But I sleep in on the weekends so it can throw it off. I just can't bring myself to set the alarm on saturday morning just to take my temp.