I bought the T-Rex to use as an everyday watch, instead of using my Garmin 945, which requires charging daily at my current activity level and when using it as a music player. Obviously, I did not expect the $140 T-Rex to measure up to the $600 Garmin, but I could not resist seeing how it would stack up. I used the indoor cycling for my spinning class, outdoor running for my running group runs, and walking for my fitness walks with my wife. For spinning neither the Garmin or the T-Rex integrate with the bike, so about all you get is duration and estimated calories. For running the Garmin offers fully customizable screens, but with the T-Rex you get what the app is set to display, but with distance, pace (min/mi), heart rate, and most important, auto-pause, I think it would fit the needs of most runners. The walking app on the T-Rex Compares to the Garmin, much as the running app, with one oddity, which make no sense to me, as the T-Rex shows the walking pace in MPH. As far as, GPS comparison, on 12-mile runs and 7-mile walks, the variation, in the Garmin and the T-Rex, was within .03 miles, so not too shabby. The T-Rex does offer an always on display, but you must choose between a pointer screen or a digital (See Photos). Then you can elect to enable the raise your arm feature to show you actual screen choice. I understand the power save feature, but I would like the option to use my screen choice for my always-on display. With SMS messages you get a notification and tapping the notification shows the sender but doesn’t allow you to preview the message. For phone calls you get a notification, as well, so don’t expect iPhone functionality. The AOD (Always On Display) and AB (Auto Brightness) are separate features, but the T-Rex lacks the important always enabled AB, during activities. When the activity occurs in non-daylight hours the always enabled AB feature is not that noticeable, but in daylight the screen is not readable until the AB kicks in, which is very annoying. Your AB and screen choice can be set to activate when you raise your arm, but there an irritating delay, even when set to the arm raise’s sensitive setting. The soft rubber band is comfortable, but I did notice while grilling, that it picked up the smoke smell from the wood chips, which was removed with a good bit of scrubbing with a scented detergent, odd but worth mentioning. With 2 hours of activity, requiring AOD and GPS, I can easily get 4 days between charges and when using it without activities, I would expect well over a week. Amazfit has obviously focused on battery life, but in my opinion, as an activity tracker, athletes will prefer to have screen feature choices for the AOD and AB, knowing that they sacrifice battery life. The internal storage will notify you when you need to sync the activity history to your phone with the Amazfit App, so there is limited storage. The music app will control the music player on your phone, but you must restart the music controller app on the watch after each change, so I find it virtually useless. Remember to install the Amazfit App on your phone before attempting to setup the watch, the app is required for the initial setup. In summary, the Amazfit T-Rex is an excellent value and a decent activity tracker, with the potential to become great activity tracker, with a few software modifications. I have received no products or compensation for my review. I am simply trying to answer the questions that I had when considering the Amazfit T-Rex and hope it proves helpful. Also, hope to see it back in stock soon.