I picked up this car dock at a Sprint store on my lunch break. It is definitely not near the quality of a HTC product. The USB port doesn't line up perfectly so you have to finagle it a bit to get the phone in. After a few times putting it in the dock you get the trick of it.
Where the HTC docks have some sort of auto locking feature this dock has an arm you have to move into place. It doesn't snap into place at all leaving the feeling that it hasn't engaged entirely. The phone seems to stay in place though.
The suction cup does feel like it will have a very strong hold. But it's a matter of wait and see if it will hold permanently without having to be re-seated. My Nexus One dock was in place for about 6 months with never having to be moved.
The positioning of the dock is not nearly as versatile as what I'm used to. The arm that extends from the base to the dock is not adjustable. It has a strong curve to it that limits the orientations that will work with any given position that you're trying to mount it. I put my in the upper left corner of my windshield and the dock ends up sticking out at least 2 inches further and more than 2 inches lower than that of the Nexus One dock.
When docked the phone does indeed launch car mode. The dock does not come with a cable of any kind. The USB cable that comes with the phone is very short so it is not a good use for the dock. Fortunately the port is standard and the cable I was using for my Nexus One dock (the cable that came with the Nexus One itself, as I plug into the USB port of my Zune HD charger/transmitter) works well. With the noticeably lower position of the dock it actually ends up being longer than I need.
So far the dock works well enough, but I wouldn't hesitate to replace it with one from HTC.
For reference I'm mounting this in my 2006 Mazda 3, which a little larger than the current Mazda 3s, inside at least.