The video portion of HDMI is simply DVI, down to using nearly every DVI pin in some position. So the converters are no more then pin and connector rearrangers. Nothing fancy, but since they are "HDTV" equipment, not overly cheep unless you try to get away from the HDTV tax most stores apply.

HDCP, the copy protection/encryption protocol works over normal DVI and HDMI plugs. Most TVs with both connectors support HDCP on both.