As an external user, you hear practically nothing or only at extreme volumes when the headphones are worn. If you take them off to make a phone call and the music continues, it is of course audible.
Subjectively, I would describe the shielding from external noise as very good for headphones of this design. But of course, inears like the Etymotik HF5 are superior in this respect. Also because there is even the possibility of adapting the pads to one's own ear (for an extra charge).
All in all, the headphones are still very good, even though they have been on the market for many years.