Road ID - Sidekick compatible with Fitbit + Garmin (Graphite, 13MM)
B-Great Ankle Band for Men and Women Compatible with Fitbit Flex 2/One/Zip/Charge 2 3/Alta HR or Garmin Vivofit/2/3/4/JR Fitness Tracker (Black, Medium)
Which Fitness Tracker Is Best For You? Apple Watch vs. Fitbit vs. Oura vs. Garmin vs. Whoop - WSJ
Garmin vs Fitbit: Wearables and features compared - Wareable