Solid wireless performance
New York City, with all its conflicting wireless signals, can be notoriously difficult on totally wireless earphones. In my two weeks of testing these in the city, I experienced only minimal dropouts and a few pairing snafus. I thought wireless performance was generally quite good -- right there with the AirPods and Jabras. However, at the end of the day, what sets these earphones apart from the competition is their sound quality.
Like other noise-isolating in-ear headphones, it's crucial to get a tight seal to maximize bass performance. I used the largest silicone tips to get a good seal and even though the earphones are somewhat large, they fit my ears pretty securely (the Jabra Elite 65t fit slightly more comfortably and securely).
Sennheiser isn't marketing these as sports earphones, but with an IPX4 rating they are splashproof and should be sweatproof (sweat contains salt so it's different than fresh water). I did use them at the gym for light workouts and some people may be able to run with them without having them fall out of their ears. I can't tell you how well they'll hold up over time if you do sweat on them a lot, but they should be able to put up with some moisture without a problem.
Great sound for totally wireless
The tonal balance is good with the default sound profile, and you'll immediately notice these have a more open, rich sound, with tighter, meatier bass than both the Jabras and AirPods. They also sound better than the, which delivers a good helping of bass but it's not as defined as the Sennheiser's bass.
This is the kind of sound you expect from a premium headphone, and this is the first true wireless headphone I've tested that I didn't feel like I was sacrificing a bit of sound quality in exchange for totally cutting the cord. The Jabras also sound good, but they're not at this level.
Aside from the sound, the Jabras are equal in all other respects -- and they have slightly better battery life and a smaller battery case. The more Jabra Elite 65t has been discounted in recent months during flash sales to $120, which is obviously a good deal less than what this Sennheiser costs. But if you want a true wireless headphone that sounds like a premium headphone, this is as good as it gets right now. We'll see what Jabra, Sony and maybecome up with in 2019.