Garmin FR910XT has R-R Heart rate data output / Fenix2 does all calcs regards VO2max, Recovery times etc but doesn't have the R-R data output compatiable with Firstbeat Athlete - hoping for this feature in future software upgrades.
Side by side visual comparision FR910XT on left / Fenix2 on right
From www.dcrainmaker.com/2014/03/garmin-fenix2-multisport.html
I dont think you can beat your your i-phone for convenience. There are some amazing fitness apps out there. I have the bluetooth heart rate monitor as well. I just start the trip logging and put my iphone in my dry bag under my suction cup cargo net and check the results when I am back from my paddle. It does drain your battery somewhat.
I use gps track recorder if I am just wanting the distances and kml. You can at the end of your paddle just select share/email.
If I am wanting more details I use mapmyfitness. Both apps are good.
Navionics is a great app for the waterways and navigation but I dont usually use it when SUP-ing.
Be sure to check out the review in issue 17 of SUPWORLD Magazine from NK Australia, they have a terrific GPS unit for SUP!