I spent a week with the most advanced fitness tracker yet, but here's why I wouldn't buy it

The Jawbone UP 3, technically speaking, is the most advanced fitness tracker out there. It has more sensors than a Fitbit or any other band, packed into a smaller and more attractive bracelet.

But that doesn't necessarily mean its the best fitness tracker you can buy - although it's definitely a strong contender.

The $180 wristband is comfortable, and when paired with Jawbone's accompanying app, offers a wealth of insights about your daily habits and health.

But there are some limitations: you need to open your phone to check the time and your stats, and the heart rate monitor can only check your resting heart rate. These are limitations that some of Jawbone's competitors, including Fitbit, don't have.

After spending a week with the Jawbone UP 3, here's what I came away with.

The basics

Jawbone's latest fitness band comes with a few new sensors that are capable of capturing more data about your health. These include bio-impedance sensors that can measure your resting heart rate, respiration, and Galvanic Skin Response (GSR). Other sensors measure your skin temperature and ambient temperature so that the band can tell when you're heating up because of activity or because you may be sick rather than just because of the temperature wherever you are. And, of course, there's an accelerometer for tracking your movement.

By comparison, the Fitbit Charge HR ($150) seems limited. It comes with an optical heart rate monitor, an accelerometer, and an altimeter, which measures altitude. This is the sensor that's able to tell how many flights of stairs you've climbed throughout the day. Both bands are water-resistant, which means they can be splashed, but you can't swim with them.

The truth is, in daily use, the difference isn't that noticeable. Both bands are able to offer different pieces of information: the Fitbit can tell you how many flights of stairs you've climbed, while Jawbone's bracelet can't. But if I forget to log my run, Jawbone's new sensors can tell that I've been doing some more intense physical activity and will ask me what I've been doing.

It's pretty accurate for the most part, too. Sometimes the app will misjudge how long I've been working out if I don't log my workout, but it usually nails the distance. You can also adjust these things manually too if you forget to put your band in workout mode.

Using it and wearing it

The Jawbone Up3 is by far the most comfortable fitness band I've ever worn - and since it's intended to be worn all day, that's really important. It's much slimmer and smaller than Fitbit bands, and it didn't make my arm itchy like the Fitbit Charge HR did.

The band is also better-looking than most other fitness band. In fact, it doesn't look like a gadget at all: it looks more like an accessory or bracelet. The model Jawbone gave me for review features a dark grey, rubbery band with a silver module at the top with a criss-cross pattern. The clasp also makes the wristband look more like jewelry than a sports band; previous Jawbone wristbands were just open so that you could slide your wrist into it.

The downside, however, is that the clasp is difficult to fasten and makes it annoying to adjust the band to fit your wrist. I can't just slip the band on in the morning and go about my day - it takes that extra few minutes of fiddling and adjusting until I get it just right.

While I love the way the band looks and feels, I'm not sure the studs on the inside of the band will appeal to everyone. You have the choice of buying the band in grey and silver or plain black, but even the black version features gold studs on the inside of the bracelet that kind of stand out. Eventually, Jawbone will offer the bracelet in several colors and design options.

The Jawbone UP 3 also lacks a screen, which means you need to take out your phone if you want to check how many steps you've walked, calories burned, and the time. I understand why Jawbone has taken this approach: it wouldn't be possible to make a band that's as thin as the UP3 if Jawbone decided to include a screen. Still, that means you can't use the UP3 as a watch even though it sits on your wrist all day.

This also means the Jawbone UP 3 lasts much longer than the Fitbit Charge HR on a single charge. I got a full week of usage out of Jawbone's latest bracelet, while the Fitbit Charge HR barely lasted for five days.

The app experience

Jawbone's UP app is comprehensive, informative, and easy to understand. One of the things that makes the UP app different from other fitness apps is that it really focuses on giving you tips and feedback, not just monitoring your health. (Note: you need to install Jawbone's new UP app for the UP3 band because the new band has different sensors. It looks exactly the same as the old app, and all of your information carries over as soon as you log in).

The Smart Coach offers up suggestions for how you can continue to meet your goals and exceed them, and analyzed the changes in your activity from day-to-day.

As soon as you open the app, Jawbone shows you a bar graph of your activity for the day compared along with your sleep from the previous night.

Scrolling through your feed will show you all of the activity you've logged recently, and there's also a menu that lets you organize your goals, see your trends charted, and check on what you're "team" has been doing.

Adding a team member is sort of like adding a friend on Facebook - you begin to see their fitness updates in your feed, and you can leave "emotions" on their updates (i.e. If I only took 5,000 steps of my 10,000-step goal, a team member might leave a sad face on my update).

Fitbit's app, however, shows you more information at a glance without having to scroll. This makes it easier to see information more quickly, but you don't get the same level of tips and advice you'd get from Jawbone.

So, should you buy it?

Make no mistake - the Jawbone UP3 is a great looking fitness band that's comfortable to wear and offers excellent battery life. But, if you like the look and feel of Jawbone's bands and just want something that will keep track of the basics (steps, calories, distance, sleep) you should check out the Jawbone UP2 instead. Technically speaking, it's the same band as the UP24, but squeezed into the smaller design Jawbone introduced with the UP3. It's only $100, which is considerably cheaper than the $180 UP3.

The Fitbit Charge HR is also a compelling choice. It's bigger, less attractive, and its app doesn't offer as much analysis and feedback based on your activity. But, since it has a screen, it's much easier to see all of your stats at a glance. Plus, it tells you how many flights of stairs you've climbed in a day - incorporating a task that doesn't necessarily feel like exercise into your activity logs. You'll have to deal with about two days less battery life though.