I already had the Medela shells and got these because they didn't have holes, as with any movement if they were full, the milk would spill. From this perspective, there are no leaks and emptying is very easy, so it serves its purpose. However, probably because the hole for the nipple is not in the center, it doesn't empty as much milk, and since the nipple is not ventilated, it's not for prolonged use. It's worth the money but I wouldn't recommend it for exclusive use as it may cause engorgement.