In my opinion, the Garmin Forerunner 35 (http://amzn.to/2w328uL) has the most features of any running GPS watch near its price point. One of those features is the Virtual Pacer. This lets you set a target pace and your watch will tell you whether you are on pace, ahead of pace, or falling behind pace as you run.
Although this feature isn’t exactly what I thought it would be based on the name, I do think it can have a purpose in your training plan.
If you have any questions about your Garmin Forerunner 35 or any other piece of gear, leave a message on one of my YouTube videos and I will do my best to help out.