All right...
if you want to skip background info, just skip ahead to MY POINT
Personally I hate devises like these. They pass themselves off as something they really aren't. I mean yeah if you know what the hell you're talking about the name tells you exactly what it is, but those people would never buy this devise... meaning those that do don't realize what they're buying.
Let's first explain:
VGA is similar to RGB, but not exactly the same as RGB is at a lower sync-rate. Furthermore RGB comes in various flavours, as well as VGA coming in various flavours. The differing RGB flavours isn't a big deal because it really only effects the place where the sync signal is held (and can be easily broken out with little to no degradation to the signal). But VGA, or better XVGA is the more annoying one.
We can plaster the name VGA all over the place as we're used to calling the DB-15 adapter the VGA adapter. But really VGA is a specific bandwidth of XVGA:
VGA contains a 640×480 (307k) signal (along with a couple other modes that tend to use less bandwidth). This is true VGA, note things like the Dreamcast VGA breakout box (which isn't an upconverter because the DC actually can be put into VGA mode which outputs a 30khz 640x480 image). All those other resolutions actually have names...
SXGA - 1280x1024
WXGA - 1440x900 (common mode for affordable LCD flat panels)
HUXGA - 6400x4800 (huge resolution... and notice the value there??? a scalar of 640x480... actually all modes are some scalar of the base VGA modes in the aspect range)
Now let's take this devise into mind. What it essentially is, is what it says it is... an upscaler! What occurs here is it takes the RGB signal that is inherent in all consoles (up to the current age... PS3 and the xbox360 have finally broken away from the older video handlers used in the past... dreamcast did as well).
All older consoles (PS2 and earlier) handled video a different way. There was a video processor that would hand off an RGB signal encoded in some manner to the video DAC. Here the RGB signal is placed into an analog wave and a sync signal that describes where the signal belongs on screen at each given point in the wave. This signal is handed out as:
RGB-SCART - no conversion past the initial DAC conversion (if any, very old consoles may handle RGB analog the entire time). The RGB and sync are sent at ~15khz... this is what is used by those in Europe with high quality SCART cables (though some SCART enabled TVs might not actually use the RGB... as SCART contains more video modes in its 21 pins).
Then the signal is placed into the YUV colour space. This is a more compressed colour space that most consumer level TVs use. It was decided upon years ago to facilitate transfer across airwaves where they needed to conserve bandwidth. This signal is then composited (combined together) into different composite signals for use... those signals are:
YUV-Component - (not commonly available) the YUV signal is placed into some YUV component space... for instance Y Pb Pr
SVHS-Svid - signal broken into the Y and UV components, most analog video encoders support this mode but for some reason don't output it... don't know why.
RCA-Composite - I DESPISE the name of this one... RCA is not the actual name (that's the name of the plug), but composite isn't either as Svid is a composite signal as well, as well as the next. But anyways this composites the Y and UV signals into one line. Hence the Red/White/Yellows
RF - the most composited signal where both audio AND video are all on the same cable. This actually isn't even done in the analog video encoder and is actually done in that break out box on all of them where the RCA video and the audio is put together. Further more the audio is made mono.
What devices like these do is take any of these signals (what ever is available, and sometimes not the best one either... some actually will take the RCA-composite signal depsite the presence of the others... just to be assholes, I don't know). It then breaks apart the signal and places it back into the RGB colour space. YUV -> RGB conversion is realatively easy and fast with very little degradation. Actually this very thing occurs in your TV because the display is inherently RGB so all these YUV colour spaces floating around need to be converted anyways.
Once in the RGB colour space the signal is then doubled (for every horizontal line, a second copy of it is placed in between it and the next horizontal line... depending on if it is interlaced or not can effect the visual quality of this). Now this doubling is algorithmically done simply... you use multiply the signal by two stetching the way from 15khz to 30khz. The copies just appear on their own. That's the great thing about analog, the curve is continuous so it stretches easily. In a digital signal you'd manually have to copy all the pixels over and you'd get a hard edge in the curve as the curve is integrated and not continuous. Basically causing blocking like if you drew a line in MSPaint and zoomed in on it. BUT with analogue signals what occurs is called "softening", the curve has been stretched so visual data from one horizontal line can end up bleeding into the next... to the human eye this looks like the image has gotten softer or vertically fuzzy.
.... MY POINT...
What is my point about all this!? Well why the HELL are you going to pay 60-100 dollars for a devise that works for ONLY one video game console when the actual work being done is not dependent upon the console itself. All it really needs is some signal fed to it... preferably an RGB signal at 15khz (i.e. a SCART cable). Now as long as your console outputs RGB (which most do) or you can hack the RGB signal out of the composite signal, and you've got it all in one devise. All you need is simple cables for each (which you can build or simply buy the RGB-SCART cables for).
Check out this website:
http://www.gamesx.com/index.php for tutorials on doing it over and over for every known console. The owner support the idea of using a TRUE RGB monitor, but it isn't necessary if you get some type of doubler that puts it into true 640x480 VGA mode.
Oh and further more, keep in mind... the PS2 outputs higher then 640x480... which means that using the YUV component signal from it will actually give you BETTER video quality then this doubler as there is NO conversion, and a higher resolution. It's not converting a small as 320x240 signal into 640x480...