Activity monitoringThis is the prime function of these devices so it's no surprise it does the job. You can set a target number of steps, and it gives you a pretty clear vibration to let you know when you're done (or you can check the number in the app). There are three lights on the front of the device, and if you swing your arm up just right (there's a knack), they will light up to show you how far you are towards your goal.
I'm not convinced that this part is that useful for athletes, though it can be interesting to see how many steps you're doing on what is supposed to be a rest day, or perhaps when wandering around an expo the day before a race. But most triathletes don't need to be too concerned with keeping their activity levels up!
It does attempt to split out 'activities' during the day (which basically means runs), and certainly going by those the step count seems accurate. However there isn't an obvious way to change the stride length, and with my legs being on the long side I get a fairly consistent 20% underestimate on distance.
NotificationsI don't really use this myself but you can apparently use the device to notify you of calls/messages etc. There are aftermarket apps which allow you to customise vibration patterns etc to your heart's content, or the official app allows more simple notifications
Sleep monitoringI was impressed with this. There's no option to tell it when you're going to sleep (like the Garmin 920xt), but its automatic detection is quite impressive. It seems to be able to spot the difference between reading in bed and sleeping. The only time I've had it confused was a 2am trip to settle a crying child - it decided that was my bedtime; it was easy to correct the 'sleep start' time in the morning.
The band makes an effort to give you 'deep sleep' and 'light sleep' stats, and even uses its heart-rate monitor to improve detection. Unfortunately it doesn't record those heart rates for later use.
Heart rateThis device has an optical heart rate monitor built in, primarily I believe for improving sleep detection; however it's quite handy for checking morning resting heart rates. The official app
At least in me, heart rate during exercise doesn't seem to be quite so useful. It just about works on the turbo, but not running. But at those times I'm generally using an ANT+ strap anyway.
Physical buildGiven that it's about 1/4 the price of even the cheapest FitBit, you'd expect some cheap rubbish. It's actually pretty smart and feels well-made. The device itself is an aluminium lozenge (with Apple-esque micro-perforations to let the LEDs shine through), and slots into a well-made silicone band - or a variety of aftermarket clips and straps. The two-part construction does mean that sweat and shower water can get trapped in between the band and the device, but this hasn't been a major problem. Whilst the device is shower-proof, and my wife has been wearing hers in the shower, I've tended to avoid doing so to avoid water build-up.
Battery lifeIt needs charging about once a month, even with a fair bit of messing about with the heart rate. Charging is via a small USB clip, and takes about two hours.
OverallI'm impressed. Improvements to the heart rate monitoring would sell it to me entirely - I dream of using Mi Heart Rate or similar apps to measure overnight heart rates accurately. However it's much cheaper than devices which don't even try to measure heart rate, and it makes morning measurement very easy. So definitely recommended.
I bought mine from GearBest