A built-in GPS (Global Positioning System), instead of an accelerometer that measures movement, will give more accurate real-time tracking information, with many GPS units informing you of the direction and distance back to your starting position.
A heart rate monitor will allow you to establish your own training zones to perform at your own best pace. A chest strap is more accurate than the wrist-based optical heart rate (OHR), but many athletes prefer the comfort and simplicity of OHR.
Many manufacturers have comprehensive post-session analysis software (e.g. Garmin Connect) via USB or wireless means (Bluetooth, Ant+ or even WiFi). You can also utilise a wealth of third-party apps such as Strava for live tracking and social media sharing.
Multisport watches offer button and/or touch screen usability to scroll through the watch’s main features. Check that the touchscreen doesn’t have a history of losing contact when scrolled with sweaty fingers or in the rain, and that data is displayed as clearly as possible.
Once you tip over the £100 price point, most models require USB charging via a charger bespoke to that manufacturer, usually clipping onto the side or back of the unit. Battery life can range from 5hrs to 20+ depending on how many features (i.e. GPS) you’re using.