Pre-review summary: I really really like this product. The review focuses mostly on the heart rate monitor because that is what distinguishes this unit from the rest. I've been doing a copious amount of research to find ways to improve my running fitness and overall life happiness. Running barefoot has taught me a lot. Better technique and more efficiency. It has also greatly reduced the amount of pain and fatigue I experience throughout the day. Proper attire helps by seeming to "disappear" from your sense of awareness, making you feel more naked and natural, and that is one big reason (among many) I run in merino wool. In spite of all of these wonderful things, overdoing it is still a real threat that can chip away at all my new found life benefits. A way to curtail the likelihood of overdoing it is to train based on your heart rate, and your heart rate alone. The idea is that if you can keep your heart rate in a certain range, which happens to be relatively low, then your aerobic physiology will develop optimally. In order to comfortably and conveniently monitor your heart rate while in motion you need a heart rate monitor. Most every heart monitor on the market uses a sensor that is attached to a strap that you wrap around your torso and it wirelessly communicates with a device on your wrist that gives you the results. IMO, the strap is functionally competent but is less than ideal. You can feel its presence, it starts to stink, it can chaff, and it will wear out and lose its elasticity. This new tomtom has the heart rate technology built into the wrist unit! It uses Mio alpha technology to read your pulse through the skin on your wrist. It uses a green spectrum light, which is a little different than the red spectrum used on pulse oximeters. Green light is a smaller wave length so it probably doesn't penetrate as deeply into the tissue as the red and therefore may not be as sensitive. This is ok, though, because it still has worked accurately and reliably for me. The instruction go as far as to say the monitor works best AFTER warmup. I figure this is because your vessels have dilated and your pulse has become more pronounced, making it easier for the unit to find what it is looking for. I have gotten some obviously bogus readings and to fix them I slid the unit up my forearm (maybe 1/4-1/2 inch) until the unit was firmly seated in place. I'm guessing it was vibrational interference that it registered from being a little too loose. When properly seated, it never felt too tight, just snug enough to leave indentations in my wrist after a 45 minute run. It didn't bother me one bit. The alarm/vibration it deploys when you are out of your set zone is nice and not too bothersome. You have many options for how you see your fitness zones. You can see them as your heart rate or as a fractional number. Easy is 1-2, fat burn is 2-3, endurance is 3-4 and so on. The GPS is as good as any. It finds the signal quickly and is very accurate, even under the moderate tree cover I usually run in (no melanoma for me!). There are a whole host of parameters you can fiddle with (pace, speed, laps, distance, etc) and the main running screen allows you to set 3 of those parameters for viewing at a quick glance. You can easily toggle through the other parameters while in motion thanks to its convenient control pad. One feature I would like to see is the ability to see the pace for each separate mile on the watch. You can see that info on the internet based software once you are back to your heavy smartphone or back home, so I forgive this shortcoming. The GPS function makes monitoring you fitness progress much much easier and quicker. It takes a lot of guess work out, too. The online interfacing is really cool (especially how it interfaces with google maps), but is not that different from all of the free apps you can use with your smartphone. It provides a thoroughly detailed analysis of your run, rich with statics and facts. You can view progress and PRs. I like the basic watch function. It looks sleek and trendy. The battery is a rechargeable lithium ion and it has a docking cradle that USBs into your computer. Undocking mine requires a little trick, but is very easy once that trick is learned. You just have to slide it off just right. Reported battery life is 8 hours if you are using both HR monitor and GPS at the same time, and 10 hours if only using one or the other. I'm sure it lasts for days just running the watch mode. I guess you'd need one on each wrist for super long ultras, lol. Just click the second one into action once the first dies, lol. The unit seem durable enough and I think it is water proof. The band is wide and secure. I can only hope it will last for years to come, but I think it should. In closing, I can sense that this device will become an invaluable training tool for me. It gives objective data and will help to monitor improvements easily. I highly recommend it to anybody wanting to improve their game. A word of caution, which could apply to any device designed to help improve performance, is to not let is govern your exercise. You are still in control and you are perfectly imperfect. You will regularly fall out of range and that is nothing to freak over. Just allow the device to give you a heads up and casually make adjustments. Remember, breath, relax and have fun!