I assume you mean the ones that have been built in the Southern U.S. by several manufacturers (not the European variety).
It would be great if someone had some hard data to share on these - a side-by-side comparison or a before-to-after comparison. Are there any liquid run-off issues would be another good question.
As I undertand it, part of the energy savings comes from running the boiler at a steady firing rate.
I might be wrong, but I don't think we have any of these in the west at the current time.