This is definitely a "your mileage may vary" solution. The "magic of twisted pair" mentioned doesn't really work as simply as implied here - and even then, it's being used inconsistently (R, G, and B are "twisted" with a ground wire, the synchs are not).
The page itself mentions that it works OK for 50 feet but even then doesn't give clean blacks.
If you are happy with low resolution, it's a cheap thing to try and see what happens. If it doesn't work for you, you're only out a few bucks.
if 800x600 works, it would be a cheap way to run my 4port KVM to my main pc upstairs, where I could use a cheap 2 way switcher, so I can either use my PC, or control all my PC's downstairs. Another use might be touchscreens, since they tend to be low resolution anyways. Just like you said, this is a YMMV solution for sure.
I actually used this method recently for mounting a touchscreen in the kitchen. It actually worked out surprisingly well. Iâ€™m running a resolution of 1024X768 with about 40 feet of shielded CAT5. I have no complaints about the image quality, itâ€™s hard to tell the difference between the factory VGA cable and the extended run of CAT5. I agree with the others who stated â€œmileage may varyâ€ but it worked well for my application.