Having used the earphones now for several months, I have mixed feelings. I bought them primarily for running since my previous JBL-earphones had a cable-break and couldn't be repaired. Unfortunately despite the reviews of other users, they don't stay in my ears. Every kilometre or so I have to push them back into the ears. I have tried all combinations of adaptors and EarFins (really systematically) without success. Maybe I don't have standard ears, and they are not good for these kind of In-Ear Wireless earphones. But the normal wired Apple earphones stay well in my ears through a half-marathon. The sound quality is great. Much better than any of the earphones I had before (even the JBL-Reflect BT). The Bluetooth connection is stable and has very very rarely a dropout. When a phone-call comes in while running, it stops the music and one can easily take the call. The caller's voice is clear and good to understand. The build quality is great and the earphone easy to operate. No wear or tear after about 300 km of running and other use while travelling. If the Sennheiser CX Sport would stay in my ear I would give it 5 stars. But since it is especially designed for sport and I can't really use it smoothly for running, I only give 3 stars.