Steam canners?

There's one featured in Territorial Seed's catalog - page 156, or here' s a link to the online info: http://www.territorial-seed.com/stores/1/Steam_Canner_P4447C271.cfm

Has anyone ever tried this type of canner? It appears to be about the same diameter as a standard canning kettle, but is only 3-4" deep. You set your quarts or pints in a couple inches of water (3 pints of water), then a very tall "lid" (basically an inverted kettle) drops over the top to create a steam chamber.

The merits are obvious - you can reduce your time to get the water boiling drastically and use less enegy to process. And it's much easier to lift jars in and out of the bath, plus you don't have to lug a heavy pan of hot water between the sink and stove. I'm just wondering about the safety - potential breakage and ensuring the contents are heated as thoroughly as a boiling bath...