Truth be told, I haven't loved previous JBL-engineered. They didn't fit my ears quite right and they were a little too expensive for what they were.
The new neckband-style UA Sport Wireless Flex ($130, which converts to about £100 or AU$175) is definitely an improvement. This is a well designed and recommendable headphone for both sports and everyday use.
Its signature feature is a "RunSafe" LED with three flashing modes, designed to warn motorists when you're running along roads at night. Paired with reflective clothing and common sense, it can provide real peace of mind.
Other sports-centric extras include "bend-and-stay flex zones" in the neckband for an adjustable fit, and a "speed charge battery" that gets you 1 hour of playback with just 5 minutes of charging time. (Battery life is rated at up to 12 hours at moderate volume levels, which is good.)
It's also worth mentioning that the earbuds adhere to each other magnetically, which allows you to wear them as a sort of pendant and keeps them from flopping around when you don't have them in your ears.
The real key to any of these in-ear sports headphones is the shape of the earbuds and tips and "fins" that are included. The fins help keep the buds in your ears and the tips should allow you to get a tight seal to maximize sound quality. With earlier Under Armour headphones, the buds themselves were a little bulky (one model had a heart-rate monitor) and not all that comfortable to wear, at least for me. That's not the case here.
I was able to get a decent seal using the largest tips of the two that are provided, but I'd like to see a set of XL tips added to the mix to help ensure more people get a tight seal.
I thought the sound quality -- for a Bluetooth sports headphone -- was quite good. The bass may not have the visceral impact of a more expensive full-size headphones but it's got some kick to it while avoiding sounding bloated or boomy. The midrange sounded pretty warm and natural, and the highs provided ample detail without grating.