For most people, single use containers are no more valuable than drops in a bottle & since they are a lot more expensive, only people who need them should buy them. You need this if your eyes are particularly sensitive or if you use drops a lot and don't want to get too much preservative in your eyes. If you only use drops one or two times a month these are a better buy since once a bottle is opened it only lasts 30 days, while single drops remain fresh until the container is opened.
TheraTears single use containers contain 6ml. Most competitors' single use containers only contain 4ml, That means you get more drops for your buck. In many cases you can use half in the morning and half in the evening - but if your eyes are extraordinarily sensitive, use the whole container all at once because by evening bacteria may have entered the container.
Nota Bene: These containers cannot be resealed.
The TheraTears website is great -- lots of scholarly articles.