I've recently stumbled upon a listing on eBay which claims to be selling VGA cables for the Dreamcast. They look legit, and they're quite reasonably priced, at $12 AUD.
The VGA box (at least the one I have) also has optional S-video output. I never use it, though, as S-video is visibly inferior to both VGA and RGB SCART.
There's no reason why this cable shouldn't work just as well as a VGA box. It doesn't require any complex parts, just a simple resistor which is probably located in that big VGA connector.
The only advantage a box has over a cable is the ability to switch between composite and VGA if there's a game that doesn't support it. The cable works amazingly well. 2/3 of my consoles had loose A/V ports. So I got a screen with black bars, but I don't think that's too common of an issue
Some of the cables can be poor quality. Mine was very poor.Cables started to fray and the housing popped loose, cheap chinese stuff. The cable you posted here looks stronger than mine and yes it makes a big difference if you are playing on a flatscreen telly,
That one works great for me, and will work on most tvs or monitors.
The only difference with the vga box had some kind of buffer circuit that Some Old CRT monitors require for corrected image. but most newer and lcd screens have this circuit built in or handle the image through software, so they do not need the vga box. some newer tvs wont even work with the vga box but will work with this straight vga cable. Its worth how cheap they are
I got that one (or one really really close to it) and haven't had an issue. The biggest advantage of the box is that you can play non-VGA games without pulling the plug out of your console. Supposedly you can switch after the VGA check on some games, but I never got that to work when I used a box.
For that price you can hardly go wrong, especially if it doesn't work eBay/PayPal will reimburse you anyway.
Personally I use the Hanzo VGA-box which is a great VGA box with an built-in scanliner, perfect for mimicking that CRT feeling on a LCD screen (http://www.beharbros.com/#!hanzo/c1gph)