I swapped out the newest Apple Watch for a cheaper model that's more than 2 years old - and there's only one thing I missed about it

Since the Apple Watch Series 3 is two generations behind the Series 5, it lacks many of the technologies Apple has introduced in recent years.

Although the Series 5 and Series 3 share many features, there are also several differences between the two when it comes to their design, display, and health-oriented features.

The Series 5 has a slightly bigger screen that occupies more space on the watch's face compared to the Series 3, and comes in new size options. While the Series 5 is available in 40mm and 44mm case options, the Series 3 comes in 38mm and 42mm sizes. At 10.7mm thin, the Series 5 is also slightly sleeker than the 11.4mm Series 3. Apple introduced this redesign back in 2018 with the Apple Watch Series 4, which it no longer sells.

Unlike Apple's older watches, the Series 5's screen is capable of staying on when it's not in use so that you can see information like the time, progress toward your fitness goals, and other data without having to move your wrist or tap the watch's screen.

The Series 5 also has an electrical heart-rate sensor, another feature that initially appeared on the Series 4. That means the Series 5 is capable of taking an electrocardiogram to help identify irregular heart rhythms. The Series 3 has an optical heart rate sensor, which can measure your heart rate but cannot take an electrocardiogram.

The newest Apple Watch inherited the Series 4's fall detection too, a feature that can tell when you've taken a hard fall and provide the option to call emergency services directly from the watch. The Series 3 lacks this capability as well.

Apple's new latest smartwatch also has a compass, which can provide more accurate location data such as the direction you're currently facing.

And lastly, the Series 5 runs on a faster processor that Apple claims is twice as fast as the one that powers the S3.

But there's only one feature I really missed after switching from the Series 5 to the Series 3.

New features like the ability to take an electrocardiogram and detect hard falls are certainly important. They make the Apple Watch more than just a basic fitness and activity tracker, turning it into a device that's capable of monitoring more meaningful health changes.

These qualities may be a deal-breaker for some shoppers, especially those who are looking to keep a closer eye on their cardiovascular health. But that doesn't mean everyone should count out the Series 3. If you're anything like me, you primarily intend to use the Apple Watch for tracking daily activity and workouts, viewing smartphone notifications and phone calls on your wrist, and checking the time — all features that the Series 3 excels at even though it doesn't have the latest features found on the Series 5.

Of all the features that the Series 3 lacks in comparison to the Series 5, it's the Series 5's larger, always-on display that's the most helpful when it comes to improving the way the Apple Watch handles these daily tasks.

When running on the treadmill, for example, I found that it was much easier to see the time and progress toward my goals by just looking down at my wrist during a run. With the Series 3, I often have to pause my run and deliberately turn my wrist or tap the display to see such information.

Even being able to just peek down at my watch to see the time, a text message, or progress toward my fitness goals as I'm typing at work during the day added a new level of convenience to the Apple Watch. Glancing down at my watch is much less of a distraction than momentarily stopping my work to turn my wrist or tap the screen.

The Apple Watch Series 5 is also just nicer to look at since there's always something being displayed on its screen. No matter which watch face you're using, it's bound to be more aesthetically pleasing than a plain black screen.

While the Series 5's always-on display is its best feature, that doesn't necessarily mean its perfect. Not every feature works in always-on mode. If you have an app open, for example, you'll still have to activate the screen to view it. This usually isn't a hindrance, but I do wish it was possible for the Apple Watch's timer app to remain on screen in always-on mode. Timers are only viewable in always-on mode as a complication on the watch face.

Here's how you should decide which one is right for you.

The Apple Watch Series 3, although it's more than two years old, strikes a good balance between must-have features and affordability. It doesn't have many of the modern features of the Series 5. But unless having features like ECG monitoring and fall detection are very important to you, the feature from the Series 5 that you're really going to be missing out on by going with the Series 3 is its always-on display.

Overall, the Series 5's always-on display makes the watch immediately more useful in just about every situation, whereas the health-oriented improvements in the Series 4 and Series 5 are critical but probably only relevant under certain circumstances.

If you're an iPhone loyalist looking for a simple fitness tracker and smartwatch, the $200 Series 3 may be a better deal than the $400 Series 5. You'll be sacrificing features like the larger always-on display, fall detection, and the ability to take an ECG, but if those capabilities aren't a priority then the Series 3 will likely suit your needs. Both watches run on Apple's watchOS platform, so you'll have access to the same apps and software-based features like activity trends monitoring, female cycle tracking, and more.