Pros: easy to use, accurate, no sticks to buy, does the work for you, can use for contraception or conception
Cons: a little costly at first, user diligence
I received my Lady-Comp as a wedding gift and have used it for both contraception and conception. Even with my some-what irregular cycles it has been completely safe for me.
The Lady-Comp encompasses the values of NFP, but does all the work for you. The alarm wakes you up and reminds you to take your temperature then calculates and stores all of your data. You get a green light on days you're infertile, a red light on days of high fertility, and a yellow on days that there may be a slight chance of getting pregnant. With its hi-tech internal computer it literally learns your cycle and can predict your fertility a few days in advance (so you can skip a day here or there).
I bought another as a wedding gift for my cousin and while it seems a little costly up front, with no sticks to keep buying it pays for itself in a matter of months and has a lifespan of 10 years or more.