Garmin Forerunner 910XT
The Garmin Forerunner 910XT is one of the better options for multi-sport training. I bought it last summer (2013) while training for the San Diego Tri-Rock Triathlon.
At first glance, its definitely an upgrade from my Forerunner 205 that has served me well since 2008. The 910 is lower profile and has a much more sensitive antenna. The 205 sometimes took 3-4 minutes to get a proper signal, whereas the 910 would catch within 30 seconds and never more than a minute. The software is also upgraded, and, with the ANT+, it can send your workouts to Garmin Connect automatically and wirelessly for analysis.
The use of the heartbeat sensor can assist your training by keeping you in the heart rate zone you need to be in. Prior to my college nutrition and fitness class, I had never thought about this type of training, nor did I have a heart rate monitor to use if I had. After the class and with the addition of this piece of equipment, I decided to give it a try. It took a few weeks to notice a change, but it did, in fact, help my training and my mileage was increasing steadily.
As for the multi-sport training, I wouldn't use any other system. It switches between sports easily and even tracks transition times. My concern was with using it in water, but that was satisfied after a few training swims in Big Bear Lake. By race day, I was ready to rely completely on it for accurate timing and distance tracking between the sports and transitions.
Its a great device and I highly recommend it!