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To answer "Gymfolks" question, I prefer the HAI switches as they have a more solid feel, and don't have the "click" sound when pressed (much quieter), but are not "mushy" like some of the old X-10 switches. And yes, all of the UPB devices work with each other across manufacturers.
However, UPB is somewhat more expensive. Comparing apples to apples, a 600W Insteon SwitchLinc dimming decora switch $40 from Smarthome, and a HAI UPB switch is $52 from Worthington.
The main reason I chose UPB over Insteon is the seamless integration w/ HAI's OmniProII security/automation panel. The configurability of these devices are amazing as well. From UpStart, you can configure all of the scenes of course, but you can also configure things like the LED color, ramp rates, and discrete actions for single- and double-clicks on each button/paddle end.
Kurt