I had rather not have a foil seal myself, I once had a foil seal go into a radiator when changing the coolant out. If they can seal a bottle with a little snap plastic ring around the top, and use a seal in the top (the foam/plastic seal) that's the way i like them. They are still tamper proof because of the little plastic ring under the top the snaps off once open. If someone was going to the trouble to get by the snap plastic snap ring, a foil seal would not be any problem either.
Clint
Clint