There is a world of difference between legal, DOT approved projection HID light system (STARR HID LIGHTS) for the Hummer H3 and the "retro kits" you find online or ebay.
The "retro kits" use the existing halogen light housing and change out the bulb for an HID bulb and include the required ignitors, ballast and wiring harness. This OEM halogen light housing is not designed for the HID bulb and the light pattern produces high amount of dazzle and is dangerous and illegal, that may or may not bother you, unless you're coming from the other direction.
The STARR HID system uses a light housing designed for HID and shines the light straight down the road and right in front of the vehicle Right where you want it most. The STARR HID system includes projection light housings, bulbs/ignitors (D1S bulbs), ballasts and wiring harness and three year warranty.

If you want to spend less money and just get the retro kits HID, that is certainly your choice.
But comparing the two systems is really an apples and oranges story.

I have had a set of the Starr HID lights for a year and they are superb. Yes, they are not cheap, but you are driving a near forty thousand dollar vehicle.
If you care, check out other posts (HID HEADLIGHTS) and you can read other peoples opinion.
Here is the STARR link, http://www.starrhid.com/