While I didn't necessarily need this cable since I modified my Dreamcast with a VGA out using it's native capabilities, I did like the idea of having the convenience for use with televisions that did not have a VGA input. There are so many helpful reviews on this cable on Amazon (take the time to read a few), here is a quick rundown from my experience:
1. The cable really does use the VGA signal from the Dreamcast and convert it to HDMI 2. The cable does no upscaling - so if your TV doesn't accept the Dreamcast's odd resolution and refresh rate which is interpreted as 640×480 VESA by most TV's, it may not work. 480p on a TV is supposed to be 720x480. Not the fault of the cable, but of the Dreamcast. 3. If your TV doesn't work and you get a blank screen or no signal message, try turning on the Dreamcast first, and then turning on the TV. You can also try changing to a different input, and then back while the Dreamcast is on and some Televisions will pick up and trigger the 640x480 signal. 4. My cable when comparing it to my VGA output was too dark and the colors were off. I took mine apart and changed (increased) the resistance on the RGB input lines. This will both add clean brightness color to your final output signal and I increased mine finally to similar values to that of my built in VGA output. To do this change the three 75ohm SMD resistors and replace them with 120ohm resistors. See my picture for reference. If you want one step down, you can use 100ohm instead, but I get some really good results with the 120ohm. 5. This cable out of the box produces a slight loss in sharpness (noticeable) compared to the native Dreamcast VGA signal. It's not bad and less noticeable on a TV compared to a monitor. It may be possible to adjust this also by changing the filtering components (usually capacitors), but unfortunately their values are unknown since they are not printed on them like the resistors.
Hope this helps someone out there that doesn't mind tinkering and isn't intimidated by soldering. I really like my Pound cable much more after I made these changes because I didn't have to change a bunch of things on my television to compensate for brightness and contrast.