I like the zip as battery pack does not slip at all. It's snug but not too snug.
I bought this for strapping a Lectrosonics wireless pack on NFL players during an outdoor videotape session for broadcast television. This fit the wireless transmitter well and protected the transmitter from heavy sweat in 90°+ heat for over an hour very hard pro athlete endurance workout. It adjusted to the player's waist size well and stayed in place. After a laundry soak & hand wash they came clean nicely. Cannot judge durability yet after only one use.