My s1 works perfectly, yes there is sometimes a variance of a few yards when you measure it against sprinkler heads, or fairway markers or stakes. I trust the s1 yardage. simply the markers are often measured not as the crow flies , but down the center of the fairway and ten to the center of the green, most fairways I play can have some jog or slight curve of the fair way as it approaches the green.
The second reasons is the measuring devices, including the personnel can make mistakes or be inaccurate. Garmin does their calculations with satellite and claims accuracy within 1 foot for 300 yards
I chose the s1 because some of the feature sets in the s2 and s3 just are not important to me. Just way too much information is given to you- most you already know from your own eye sight. IMO