If you want to measure your trips and performance, it’s true that there are a few options. There are GPS watches or your smartphone itself as other options. However, they have been specially designed for the job and often these other devices aren’t as accurate. You can get a mount for your phone but stability and water-resistance are concerns – regardless of what you’re willing to spend, most people have spent hundreds on their smartphone! It will also use up your phone battery faster than simply connecting to an app in the background. Some watches can double up with a special mount, but otherwise, it’s on your wrist and not in front for quick glancing and ease of use.
Remember that smartphones will take up more room and the screen may not stay on when not in use. If you do configure them otherwise, bike apps will drain the battery. A phone is still an important piece of equipment, especially if you have a less sophisticated device and have no other form of communication.
If you can’t see why you need all of the functions in a high-specification model, then the very reasonably-priced basic models will suit you fine.