First let me say I'm not a triathlete, so I only use this for running. If you want a detailed review there's plenty elsewhere.
I've given this 3 stars because when it works it does what I'd expect it to do - tells me where I've been, how far, how fast, heart rate etc.
But it has some really annoying features.
1. If you switch it on and then don't start the activity for a number of minutes it switches off - saves power I guess, but if you're waiting for the start of a race annoying at best.
2. So you press start and mostly it starts - 3 stars, but occasionally it's lost signal (maybe you had that final trip to the toilet).
At this point it informs you it doesn't have a GPS signal and asks if you want to start the timer anyway. Actually no, I'll ask the starter to get everyone back and we'll all wait while I get a GPS signal.
3. And if you do decide to start it without signal it'll take about 2 miles before it picks one up - just doesn't like fixing on a moving target I guess.
4. What happens when it loses signal when you're running? It just starts measuring from where it gets the signal back. A garmin will assume you've travelled in a straight line between the place of the last signal and the place the signal is regained, which seems a much better solution.
Oh, and the Garmin 310XT will give you a UK grid ref which could save you're life when you're lost out on the fells.
So come on Timex catch up. And maybe get someone to actually test these things.