I have a five and a fifteen count otterbox.
I have never bothered "charging them" since I only use them for short term storage, and they are quite airtight, so your smokes will stay very well.
The purge valve, IMHO, should be standard on all of the sizes. IF you take it on a flight, you'll have a hell of a time opening it when you land unless you can relieve the vacuum that will be created inside. I opened my 15ct several times (was a carryon) during a flight and each time was pretty tough.