I don't have the Fit, but I do have the Gear 2. I have been running with it the past week and I will say that the heart rate monitor is not very accurate if you're going hard, but it is quite accurate when lightly jogging or briskly walking. I didn't get the Gear 2 primarily for fitness but it is a nice thing to have. The calories burned and and other stats seem to align nicely with what the treadmill tells me, but the heart rate is often wildly off after sprint intervals.
That being said, I think the Gear 2 is pretty awesome, a big improvement in appearance over the first generation, and great for notifications.
Also, someone may have mentioned this earlier in the thread, but if you want to buy a Gear 2 or Gear fit you can get them for 25% off at AT&T's website. You just need to add two cheap $5 cases to your order to take advantage of their buy 3 accessories and save 25% promotion. I bought my Gear 2 there and saved $75 on it.