These headphones are incredible! I bought them to replace a pair of Motorola Bluetooth headphones that I bought on Amazon. I'm an extremely heavy sweater and the Motorola's stopped working after only two weeks. I've had the JayBirds for almost a year and a half and they're still going strong!
First, they almost never fall out of your ear. I do a lot of Crossfit and the only time they start to come loose is when I'm jumping rope for an extended period of time. The "waffles" really help hold them in place.
Next, they stand up to excessive sweat extremely well. I'm in the Army and was deployed to the Middle East for the last eight months, through the summer months when the average temperature was over 120 degrees. And through that heat and my sweat, these headphones still work with zero issues.
They also work okay across a gym. I can set my iPhone down next to a rack and walk around the gym pretty freely without losing quality or the connection.
The only reason that I gave them four stars and not five is because there isn't a battery indicator on them. So you may end up losing music in the middle of your workout due to the battery dying. But honestly, that's more my problem than the headphones - I could have charged them every three or four days regardless of whether or not they needed to be charged.
I would definitely recommend these to someone looking for quality Bluetooth headphones.