I've both, and there are some differences, but not all in Instinct's favor tbh :).
Instinct is lighter, easier to sleep with, and the HRM is a bit faster to react and more accurate than the older one. (it's the same one as in the F5 - 2nd generation OHR from Garmin). Battery is not that great, but it's ok.
F3HR has the advantage of having real storage (not the 8/16 MB *** that instinct has) and can install apps and watch faces. Compare that to Instinct's no upgrade route (no access to any extra apps, data fields, watch faces). Unfortunately F3's is compatible only with the old Connect IQ platform, it can't use/install all newer software (connect 2.0 and 3.0 platforms), but at least it has the option.
Instinct is ok if you're the type that doesn't want to change anything and use a watch as it is (with no extra liberty allowed).
