I just got my 235, so wanted to take it for a test spin and comparison. I put my Garmin HR strap on to use with my Galaxy S5 and Endomondo like I usually do, and had the FR235 on. I never paired the HR strap with the FR235. However, it apparently picked it up and used that! So much for that comparison. Are pairings between Garmin devices automatic? Some discussion about pairing the FRs with a footpad (either here or on DCRainmaker) had me think it wasn't automatic, and not necessarily easy either.
By the way, newbie here on the Garmin Running/Forerunner part of the forums. I might have had some posts in the old Geocaching section, can't even remember for sure now. Hi! ;-)