For biking, behaviour is very similar to running, with GPS tracking of your location and elevation against time. Your biking information will be greatly enhanced by the optional addition of the cadence / speed sensor, giving you details of how fast you are pedalling and the resulting wheel revolutions, although we weren't sent this accessory for our review so can't comment on the Multi-Sport's abilities in this area.
For Swimmers, the Multi-Sport tracks the number of lengths you do, translates this into distance via the length of the pool, and also records both the number of strokes you make and their type. This makes it broadly similar in abilities to the Garmin Swim. The latter had a few issues with stroke detection when it was first released, but later firmware releases have alleviated this almost completely.
Using GPS to track swimming is not really practical even in an outdoor pool, and impossible in an indoor pool. So the Multi-Sport employs its built-in accelerometer, which TomTom calls the Indoor Tracker, to detect your swimming. This is exactly the same as the Garmin Swim, but in our testing the Multi-Sport proved far less accurate than the Swim was even when it was launched.
We tried a test set of 50 lengths of a 25m pool, with one watch on each wrist. The Multi-Sport has a setting for when you are wearing it on your right wrist, which we had enabled. The Garmin Swim recorded 51 lengths, with the extra length due to an accidental collision with a barrier between the lanes. The Multi-Sport, however, thought we had managed 79 lengths, which was flattering but pretty much unusable.
Whichever sport you perform, you can apply some structure to your routines via the Training section. You can set yourself distance, time and calorie goals. You can set up intervals, and record laps either by time, distance or manually. For running and cycling, you can configure training zones, with pace and heart rate available when running and speed, heart rate and cadence when cycling. You can also race against a previous session when running and cycling, which is a great way to use yourself as a training partner.
Our biggest criticism of the Runner when we reviewed it was the software used to track your workouts. TomTom's own MySports website is still in beta, but you can use the MapMyFitness site as well. The TomTom MySports applet will upload your data to both services simultaneously every time you attach it via the USB dock, and also apply any firmware and QuickGPSFix updates that have become available.
Both the MySports website and MapMyFitness provide roughly the same data about your runs, although we prefer the way MapMyFitness superimposes the Pace, Elevation, and Heart Rate graphs (if you have the latter sensor) on top of each other so you can see how they affect each other more easily. The cycling readout is similar, with speed instead of pace, and the addition of cadence information if you have this sensor.
So there's more than enough detail available to get a good analytical idea of how your workouts are working out. The swimming information, however, is nowhere near as detailed as that available from Garmin Connect with the Swim. There is no length-by-length breakdown, stroke data or SWORL, although it appears the watch itself does capture this level of detail. It just isn't being transferred to the online services yet.
If you're a keen cyclist and runner, the Multi-Sport makes sense as an alternative to separate devices for each of these activities, assuming you haven't yet invested in any ANT peripherals. The one-button system makes it supremely easy to use. Keen swimmers, however, will be disappointed, although TomTom is likely to improve the Multi-Sport's performance in this area, as Garmin has considerably with the Swim. The amount of information on TomTom's MySports or MapMyFitness is also less for swimming than other activities.
TomTom's Multi-Sport is great for runners and bikers, but needs a firmware update before it can accurately track your swimming as well.