how accurate is Mobile Me "Find my iphone"?

We grain farm and it seems like we periodically loose our phones in the middle of a field. Is is worth subscribing to Mobile Me so that I can add the "Find my iphone"? We might know that it is in the field somewhere, but we need the locater to be accurate enough that we can actually find it in the stubble. If it only points to the 1/4 section that we need it won't be that valuable. Can anyone tell me if it is worth adding in our situation?