Plain answers about distance-measuring devices: how golf GPS works, how accurate a phone really is under open sky and under trees, what a laser rangefinder does better, what the Rules of Golf allow, and what free apps usually cost you in ads, accounts or subscriptions. We build a GPS app, so we say so, and we also say where a laser wins. Every accuracy figure is attributed to its source. Read these before you spend money on a device you might leave in the bag.
Phone GPS is typically within about 16 feet of your true position under open sky, per GPS.gov, and the green center on the map adds its own error. Both are smaller than your miss from 150 yards.
Retailers say yes. The honest answer depends on how tightly you hit your approach shots, and for most golfers the number that matters is the middle of the green, which costs nothing to get.