I upgraded from the Vivosmart 3 and I am excited about most of the upgrades made in the 4. I love that we now have a button to get into the second level menu or go back to the home screen. It has a nice sleek look. It is a little narrower than the Garmin three. At first, I disliked reading the scrolling text but after a week I adjusted and it no longer bothers me. So I think the new narrow design is a plus. I had hoped I could use the Garmin 3 charging cable but the charging connection now sports an extra prong making it incompatible with the Garmin 3 charging cable. But it holds a charge much better than the 3 ever did. I only have to charge it once a week now instead of the begging and end of the week. And I use the nighttime SPo2 feature. I love the pulse ox. I've seen a lot of reviewers complain about it. Unfortunately, all of the reviews I watched or read about only used the Garmin for two or three days and at most, a few, used it for a week. This is not enough time. First, I tested the pulse ox feature against a finger pulse ox monitor. The Garmin is typically read 2% below the finger pulse ox. On a separate occasion when I was cold, it read 4% below the finger pulse ox. It shouldn't be a surprise that a wrist-based pulse Ox doesn't match the doctor's office device. However, it's within an acceptable range for me to use it. Especially, when I see I dropped down to 73 a couple of times during the night. One of the things to note is that you do need to wear this snug to the wrist for the HR and the Pulse Ox to work ideally. Many of the reviewers when they showed it, they were not wearing it snug. I can still fit my index finger between my band and wrist so it isn't tight. Another sore point in most reviews is the overnight SPo2 monitoring. This frustrated me for the first week as it has many reviewers. But after that, it worked consistently. I learned that it only runs for about the middle 4 hours of your sleep time. Now, if you are a restless sleeper and move around a lot or get up, it will stop reading. In order for it to take your Pulse Ox your wrist needs to be straight. If you bend it, it will stop reading. If you make a fast move, it will stop, if you get up, it will stop. But, once you settle again, the Vivosmart will start back up again. If your band is loose enough to slide around, you will not get a consistent pulse ox at night Especially if you move around. I also tested the Heart rate feature at the doctor's office and it was always dead on. Not once has it strayed from the doctor's reading. I tested both the pulse ox and the HR at five different doctor's offices. So I am fairly confident in the Garmin Pulse Ox and Heart Rate readings. But again, it needs to be snug to your wrist in order to achieve an accurate reading. When it is loose, it can be off. I did have to work a little to get my custom step size just right before it would take an accurate read of the distance I traveled and the number of steps I've taken during the day. For those who want to put it on and not worry about, you may or may not have an accurate measure of how far you've walked/run or the number of steps you've taken. I do feel my Vivosmart 3 was a little better there. Not sure if it's specific to my band or why it is. But I did get it to work perfectly through the custom step and matching it to a handheld GPS to confirm distance. The Body Battery is an interesting and unique feature. This one really needed time to learn me. It took a couple of weeks for this one to mesh with my life and activities. Once it did, I've found that it has been useful to make decisions on working out or not. At one point I couldn't figure out why my reading was 44 because I felt great. Well, the next day I was sick. If I had looked at the hrv and pulse ox during the day (you have to manually ask it to take the pulse ox), I would have realized I was getting sick and could have adapted my activities for the day. I certainly don't use the body battery a lot but I do find it useful. For those who like to auto-count workouts, I've enjoyed that feature quite a bit. I don't run, but I love to walk and I swim, which is why I decided on the Garmin Vivosmart 3, it was waterproof. It misses a stroke or a rep here or there but it hasn't been very often. And if you do find it missed something, you can certainly add it in the App. Yes, it really is waterproof. I use it in the pool all the time and don't worry about it in the shower. Garmin says the Vivosmart is waterproof up to 50 meters. And yes, it is! I don't normally scuba dive with it on. During the last trip, I forgot to take it off before climning into my gear. My husband was about to head below deck so I handed it to tuck it away in our bags. He dropped in his shorts pocket and well, yes, he forgot. So, this wonderful little band survived a thirty minute, 40-meter dive. It's not a dive computer and I probably won't wear it diving again because I can only handle so many wrist-based devices but I certainly won't be worried if I forget it again. So, whether you want it for the gym, running/walking, swimming, snorkeling, take it scuba diving, tracking sleep, this little wearable is an excellent choice.