I've been using the BASIS wristband for about a month.
The most important arguments FOR the Basis:
a) it's unobstrusive: just use it instead of your normal watch and wear it every day. you won't lose it and you don't have to do much, you don't even have to take it off to charge or sync it
b) long battery life: charge/sync for 10-15 minutes a day while sitting at your computer and you're fine, if you don't have a computer or USB power it'll go 4 days easy before it'll run out
c) well done web-interface. They figured out some really nice ways to graph the data and has some useful metrics
d) a LOT of data for a wristwatch: it has optical, GSR, temperature and acceleration sensors to measure heart rate, perspiration, steps and consumed calories, it abstracts from this data how long (and well) you slept, when you went to bed, when you rose, whether you take a morning / evening lap, how often you awoke during the night and how many times you stand up and walk few steps while sitting on your desk.
e) HR measurements are relatively accurate if you don't move: http://psychologygeek.tumblr.com/post/52500859364/comparing-the-basis-wrist-band-to-a-research-grade
And some arguments AGAINST the BASIS:
a) ability to measure heart rate is heavily affected by movement artefacts. This is something that can't be overcome easily using optical methods. (Buy a pulsesensor.com sensor and look at the raw data and you'll know what I mean.) However, the sensor weeds out most, but not all false values. But be aware that this means that you can't use it well for athletic activities, thus it really might not be well suited for your purpose.
b) you don't have any access to your data except via their interface. This is kind of a hit in the face for most of us. https://github.com/dunn5/MetricsCSV check here for a solution
c) gamification vs function: some of the above mentioned features, like info about when you went to bed or when you got up, are only available after you've completed 'habits'. You have to set yourself goals (walk 8000 steps a day, burn 2000 calories). If you've kept the goals you set for a while you get points. With the points, you can buy new metrics. After more then a month, I still can't count morning laps. Arrrrrr! Nice idea, it might be actually doing something for some people. Others might set their goals lower because they want the metrics. The worst part: The metrics only assess data from the point where you bought them, and not retrospectively. So any morning laps I do now will be lost forever...
d) awful display. just bad. really bad contrast, really hard to read during the day. uugh.
e) it's a bit pricey (199 USD)
f) another limitation of optical methods is that HRV is really hard to assess reliably. this option lacks and is probably not coming soon.
So if you want continuous HR measurement without hassle, the BASIS is my first choice AT THE MOMENT.
If on the other hand, you want a device the measure while doing athletic activities, go for an ECG sensor strap (look for the ability to extract HRV data if you want more from your device).
To be honest, I love my BASIS it does many things right. But you might want to wait for the next generation to come along.
There's another gem: the http://www.op-innovations.com biosensor. It's a bit in-development still, but it's just an excellent product that records 11hrs of raw data, (1ch EEG/ECG, temp & 3D acceleration per sensor, you can use several at once) is open-source, has some software to go with it and comes at a price you can't beat. (And there are still plenty arguments for it I haven't even mentioned.) If you're comfortable with handling raw data, give it a try!!!