Which brings us on to our biggest and perhaps most contentious point. While it won't deter every athlete, the biggest shortcoming of the RCX5 for us was the lack of built-in GPS. We understand this makes the watch lighter and slimmer for the times when you might not want to use GPS, for instance if you are swimming or on a treadmill, but we prefer the more integral approach.
Unlike running with the Nike Sportwatch and the Garmin Forerunners models, RCX5 owners who want to track their route have to carry the G5 GPS sensor as an extra accessory. This can be worn on an armband, or we found it worked equally well in a rucksack on a hip belt.
If you will always want to track your run on a map after a workout, this feels like extra equipment to have to carry, especially if you run with a phone or an MP3 player on your arm already.
What we can't complain about is the RCX5 's efficacy as a training tool. Using the included heart rate monitor, we were able to focus on keeping our heart rate under 160 beats per minute to run below 80 per cent of our capacity. This allowed us to run further without burning out and we set a personal best for a half marathon, something we had never managed when training with a standard GPS watch. Measuring speed alone regardless of heart rate ignores the fact that running up a hill at a consistent speed is tiring and will wear you out sooner over a longer distance, whereas running at a constant capacity is running smarter.
On the plus side, the absence of a GPS unit means regular runners don’t have to charge their watch at the mains every week. The standalone G5 GPS Sensor charges via micro-USB and the battery lasts 20 hours, but the S3 Stride Sensor and the RCX5 watch itself take a CR2032 battery which lasts between 8 and 11 months.