There are three categories to consider when buying distance measuring devices to aid your golf game: rangefinders, watch/hand-held GPS units, and swing analyzers.
Rangefinders help you find the most accurate yardage to a selected target. Simply "point and shoot" at the flagstick, and the laser will give you near-exact yardage to the hole from your position. Rangefinders have a number of options, including: maximum range (the yardage the rangefinder is capable of), maximum magnification (most offer anywhere from 4x to 7x magnification), battery life, size, display and whether it has slope or not. Slope is a feature that factors in extra yardage for uphill shots, or takes yardage off for downhill shots. Use of the slope feature, is not legal for USGA championships, but using a rangefinder without slope was made legal for USGA qualifying and amateur championships in 2014.
Watches and Hand-held Golf GPS Units:
These units offer GPS yardage to the front, middle and back of the green. A view of hazards along a hole, help with club selection based on multiple points and Bluetooth connectivity are a few benefits of GPS units. When selecting a hand-held GPS device, it's important to look at size, battery life, pre-loaded courses, courses available for download, color vs. black-and-white screens and subscription fees.
Golf Swing Analyzers and Launch Monitors:
Since swing analyzers can be specific to parts of the swing-path, tempo or even putting - you need to narrow down what part of your game you're looking to improve. Next, your intended analysis will help determine placement of the equipment. For swing speed and tempo, the monitors are normally placed in the butt of the grip or attached to the back of a glove. If you're looking to measure angle of attack and more impact-specific stats, the measuring device will be attached to the shaft of the club. It's also important to note that analyzers are specific to Droid or iPhone, so make sure you purchase the device with the correct operating system.
Launch monitors use high-speed photography and radar imaging to track ball speed, spin and launch angle to give you feedback about your golf shots. Most launch monitors connect wirelessly with compatible devices to provide real-time feedback on a number of elements. Since different monitors require different placement, it comes down to personal preference whether you purchase a monitor that has to be placed behind the ball or next to it. If you're looking for at-home data to help you dial in your distance, a launch monitor can be a great tool.