You can choose from five different watch faces for the Charge 3, making it less customizable than the Ionic or the Versa. Those smartwatches have the advantage of running Fitbit OS, which includes a library of many third-party-developed watch faces. The Charge 3 isn't a smartwatch, so its version of Fitbit's software isn't as robust as what we see on the Ionic and the Versa. It's not as critical for the Charge 3 since it isn't designed to run more than a few basic apps, but those looking for interesting watch faces will have to do with just a handful of options.
Wirecutter writers have been researching, testing, and writing about smartwatches since early 2013, just after the first Pebble watches were shipped to Kickstarter backers. I’ve personally worn nearly every notable smartwatch since that first Pebble and have written about them for a number of publications, including IT World and Fast Company. I also have extensive experience with Android phones, having written the (since outdated) Complete Android Guide and numerous articles about Android. I also contribute to and help edit the Wirecutter guide to the best smartwatch for iPhones.
In 2003, Fossil released the Wrist PDA, a watch which ran the Palm OS and contained 8 MB of RAM and 4 MB of flash memory. It contained a built in stylus to help use the tiny monochrome display, which had a resolution of 160×160 pixels. Although many reviewers declared the watch revolutionary, it was criticized for its weight (108 grams) and was ultimately discontinued in 2005.
The top smartwatches that debuted at the 2017 Consumer Electronics Show included the Casio WSD-F20, Misfit Wearables Vapor and the Garmin Fenix 5 series. Apple released on September 22, 2017 their Apple Watch Series 3 model which offers built in LTE cellular connectivity allowing phone calls, messaging and data without relying on a nearby smartphone connection. 
But the Ionic, the first of Fitbit's devices to include an SpO2 monitor, came out more than one year ago. It's frustrating to hear about exciting features that are "coming soon," when "soon" ultimately means not weeks or months, but years. While I understand it takes time and effort to develop features like this (especially if Fitbit hopes to pursue medical device clearance or approval from the FDA in the future), I don't think Fitbit should hype features that it isn't ready to let users put to the test.
It's also very bulky. Sitting at 46mm wide might not sound like much, but then you have the depth, and there's a lot of it here. In fact, if we had to pick one criticism of the Watch Sport it's that it crams so much in, it does so to its detriment. The size will be too overbearing for many, but the pay-off in size means that most of the great features of the Watch Sport have been discarded.
The LG G Watch, Samsung Gear Live, and Motorola Moto 360—the Android Wear models—have intuitive color touchscreen interfaces and were judged easiest to interact with. The Martian Notifier, Cookoo 2, and MetaWatch M1, which have push-button navigation, were determined to be the most difficult to use. In particular, the Cookoo 2's buttons were very hard to press.