eBay with Clever Training has the Garmin Fenix 5 GPS Multisport Smart Watch w/ Elevate HR Technology (Gray w/ Amp Yellow Band, 010-01688-02) for $450 - 20% off with coupon code PICKDADSGIFT [Exp 6/6 at 7PM PT; requires Paypal] = $360 with free shipping. Normally $450+.

Has a performance widget that shows the effects and progress of your workouts right on the screen as you go.