Reading through the comment thus far, I'm seeing a lot of negative sentiment towards the product. In the end, the demographic of the type of people on Hacker News is still vastly different from the majority.
I don't think it matters that refusing to integrate with Healthkit or rejecting data through their API matters. Check out the App Store. The Fitbit app is usually in the top 100 apps, let alone tops in the health category.
Some of you are bringing up the Apple Watch or products from Garmin and such, but again these are completely different. I recently got a Charge HR myself from fitbit and the requirements for me were some base functionality, acceptable battery life, and above all size and lightness. I've had the Charge HR for about 3 months and I hardly notice it except when I'm in competition with friends on the Fitbit app. I've had more than just a handful of friends also getting Fitbits because of the ecosystem.
I'm a believer, and barring a ridiculous price after the IPO, I'll likely be an investor.