|Top to bottom: |
Prepara Evak mini (glass), Airscape Lite (plastic), Airscape original (stainless steel)
Basically, they are an airtight vessel with a lid that slides down inside the canister, and rests on the surface of the coffee, thereby shrinking the size of the vessel to always fit - exactly - the amount of coffee you actually have. Think about it - regular airtight containers trap both air and food inside. Which will keep your food fresher, a container filled very full, or an almost empty one? It's the equivalent of sucking all the air out of a ziplock bag.
The canisters are more complicated than that. The lids have a one-way valve built into them, that allows the air to escape as you collapse the lid into the vessel. It also allows any gasses released by the beans to escape as well, but doesn't allow air back in. It doesn't create a vacuum.
Airscape was the first on the scene, I think. The original canisters were made of stainless steel, which is great for folks who store their coffee out on a counter, as they are genuinely light-tight. The inner lid has a hinged handle - when it's upright, the valve is open, and allows air to escape as you push the lid down until it touches the surface of the coffee. Then you rock the handle sideways so it lays flat against the inner lid. Handy if you need to fill the canister very full. It has an outer lid for additional freshness. The first generation had a second 1-way valve on the outer lid, but newer ones do not. Not sure the valved outer lid was necessary or not, or why they chose to eliminate it.
They now have a "Lite" version, which is made of plastic. I use these the most - I like seeing the beans through the plastic, and as much as I avoid brewing in plastic, storage of room-temperature beans in plastic isn't a problem for me. Plus, they come in a square version, and it fits in my coffee-storage bin better (to help contain the smell for my coffee-hater). Airscape does offer a glass version, now as well, though I imagine they work just as well. I prefer the Airscapes, because I store the coffee label between the collapsing lid and the outer lid. Especially cool, is that Airscape also offers a big version of their collapsing lid for use inside buckets, not that that is especially helpful for coffee. :-)
The Prepara Evaks only come in glass (so far as I know), and the lids meant for coffee are lined with stainless, so that only inert materials touch coffee (they do have plastic parts above the layer of stainless, however). The Evak collapsing lid handle doesn't lay flat though, which means if the canister is very full, the handle will stick up out the top. My favorites of these are the minis, which are GREAT for taking a day or perhaps two of beans with you for traveling. No outer lid, though. I doubt the outer lid is necessary for freshness, but I like it as a convenient place to store my coffee label. If you have your coffee lined up on a shelf, you can still set the label above the collapsing lid. It's just that my Evak gets stored sideways inside a plastic bin (it's tall and thin, rather than short and squat like the Airscapes), and the label falls out. Not in itself a big deal, except that I'm sloppy about putting away my old coffee labels from inside the bottom of my coffee bin, so if it falls out, I might forget which label is the correct one (well, probably not. I just like the additional lid, even if I doubt it's necessary for bean freshness). The Evaks also offer long-handled scoops that hook over the top edge. These are handy if you get the especially tall/thin versions of their canisters.
The canisters from both companies (but not the collapsing lid) are dishwasher safe. The collapsing lids should only be wiped clean.
If you go through coffee quickly - these might not be necessary, as they really only offer modest improvements over a jar or ceramic crock for bean storage. And they are expensive ($10 for the Evak mini, $20-$25 for bigger sizes). But every bit helps in my opinion.