The watch works well for all triathlon activities. Have used it for open water and pool. The only issues have been with the wrist HR sensor. The sensor is not as reliable as chest strap, and sometimes the watch needed to be power cycled to activate it.
This watch has solved every problem I've had with GPS devices. It finds satellites quickly, it is accurate in the pool and open water. I have problems with my vision and have no trouble seeing any of the screens. Easy to change options without hitting strange button combinations or putting your reading glasses on. Instantly uploads to my phone and computer. Extremely long battery life. I haven't used it in a triathlon yet but have practiced that function in training and am confident that it works. I love this thing.
I have an Edge 820, which I use for cycling. I'd been running for a while using the available watch and phone based running apps. Most were adequate but suffered two giant flaws, the GPS tracking was poor and HR readings erratic in anything but ideal conditions. Sure it made me feel great that I could suddenly run a 4:00 mile and elevate my heart-rate to 210 but that wasn't helping my training. The Forerunner 745XT offers support for GPS and GLONAS, wrist-based HR, and impressive battery life in a relatively small and lightweight package. It's great to be able to leave the phone home on race days and pairing with the optional HR Run provides useful feedback on my running mechanics, including cadence, balance, vertical occilation, and stride length. It looks a little cheap and plasticky but it's a sports watch, not a fashion accessory. The software is good and the connection to Strava is dependable.
I purchased the 735XT after returning a Fenix 3 HR. Fenix 3 HR was great but huge and heavy. With the 735XT, I mostly forget I am wearing it. It also replaces a Garmin Edge 800 because I like the automatic upload of activities.
Works beautifully with Garmin Vector and Trek BLEAnt speed cadence sensor.
I highly recommend the No Frills watch face from the Garmin IQ store. I have the No Frills watch face and have set the color scheme to be inverted which makes it much more visible.
I've had the watch for a month and had to send it back to Garmin for a replacement. After 6 emails back and forth and trying step after step to get it to work Garmin finally agreed to send a replacement.
Great watch but Garmin support has much to be desired.