Comfort: I deliberately chose the flex 3 after looking at the JBL site to see what the differences were between flex, buds and beam. These flexes are not in your ear, which has the great advantage that they fit very comfortably and you notice that because you do not feel them, even after a few hours. You also hear a little more ambient noise, which I personally like. If you want to be more isolated from your environment, want a little more bass and need better noise cancellation, it is better to choose the beam or buds. These sit in your ear and therefore close your ear canal better. For me the flex are just ideal. (I've also had wired in-ears, but I just don't like them as much if you wear them for longer)
Functionality: many useful functions such as options that you use when making phone calls or if you meet someone on the road, the sound in your ears is automatically muted, you will find earplugs, measuring your own ears, operation via the storage/charging box, app or on the earplugs themselves, various equalizers and much more.
sound quality: very good in this price range. Voices and instruments sound very 'real' and clear/easy to understand and can be placed/positioned well, no sharp tones or the like, depth of bass is good. The width image is good, depth could be a little better. The point where earsets that last twice as long are slightly better are the dynamics, but I prefer this live flex 3 over my wired headsets. The drivers used and sound quality are simply off. Also works well with the hi-res streams from my Tidal account, something Spotify is slowly starting to realize
The battery life is more than sufficient, I have not yet encountered the limitation that they played empty and the storage box also works as a charging station (and has a battery). The earplug and box come fully charged out of the box. I just had to update the firmware, but that's very easy once you've paired them with your phone.
The only area for improvement is that you can only have 2 devices connected at the same time. That's quite a shame because I would like to connect my phone (mainly used for music and calling) and iPad (for watching TV, videos, etc.) and my laptop (for team meetings). I hope this will be added in a future firmware update