The vacuum canisters and domes from NewMetro Design are great for things you want to seal, but that you also want to have regular access to. Like a cake or loaf of bread or maybe that bag of whole wheat flour that you're always dipping into.
The idea with these containers is that the vacuum is part of the container. You press a big button on top, and the vacuuming begins. It stops automatically when the vacuum is complete. To open the container, you pull the button out, and the vacuum releases.
The really cool thing about the dome is that you don't need to use the base that comes with it, as long as you've got a smooth surface. So if you wanted to, you could put the dome over a cake plate on your smooth counter, and seal the dome right onto the counter.
The first test of the dome was a coffee cake. I left it unwrapped, on a plate, and under the dome. What I thought was interesting was that the cut edge of the coffee cake didn't dry out. I had the same result with a loaf of bread - the cut end didn't get dry and crusty while it was stored, as it would have in a plastic bag.
The vacuum uses C batteries, but both the canister and dome I tested came with adapters to used AA batteries as well. The vacuuming wasn't super-fast, but it's not like you need to watch it while it happens. Just press the button and walk away.
As far as how well it holds a seal - well, that takes care of itself. One evening, I heard the sealer activate itself. I'm not sure what caused it to do that, except that the temperature in the room had just changed significantly. Once it had vacuumed again, it stayed sealed until I opened it. It was a little spooky when I heard the unexpected noise, but it was better than having it unseal.
The large oval dome is pretty darned big (interior space is about 10 1/5 x 18 1/2, and about 5 inches high) and I'm finding it pretty darned useful. I can store a really large loaf of bread in it, or several smaller items.
Battery life seems pretty good. I accidentally left the dome vacuuming over night while it wasn't on the base (don't ask) and it was still valiantly attempting to vacuum all the air out of the house in the morning. Those batteries are still functioning several weeks and many vacuums later.