TL;DR: there is little point in upgrading to the HRM-PRO Plus from the HRM-Pro, other than a new battery door there is nothing to differentiate between Garmin's top 2 heart rate monitorsTL;DR: there is little point in upgrading to the HRM-PRO Plus from the HRM-Pro, other than a new battery door there is no difference.
Garmin HRM-Pro Plus Heart Rate Chest Strap - bike-components
Review: Garmin HRM-Pro Plus
Garmin HRM-Pro review
Garmin HRM-Pro Plus Heart Rate Belt - Running Watch - Heart Rate
Garmin HRM-PRO Plus Heart Rate Strap In-Depth Review
Garmin HRM-PRO Plus Review - Quick Look and Comparison HRM-PRO vs
Garmin HRM-PRO Plus Heart Rate Strap In-Depth Review
Review: Garmin HRM-Pro Plus
HRM-Pro Plus - Heart Rate Monitor, Sports & Fitness
Garmin HRM Run, Dual, Swim, Tri and Pro Compared - OneManEngine
Garmin HRM-PRO Plus Heart Rate Strap In-Depth Review
Garmin HRM-Pro Advanced Heart Rate Strap – In-Depth Review – DesFit
Garmin HRM-PRO Heart Rate Strap In-Depth Review
Garmin 010-12955-00 HRM-PRO, Premium Heart Rate Strap
Garmin HRM-PRO Plus Heart Rate Strap In-Depth Review