I own a XRGB-3 and a Kworld PRO WSHD TV, and I also have a kworld x1920 (
http://www.tigerdirect.com/applications/SearchTools/item-details.asp?EdpNo=3655607&CatId=1427 ) gamer's choice edition.
XRGB-3 is hands down the best, and worth the extra money to me. But if you are
not looking to spend 300+ then the kworld x1920 is a good choice. the PRO WSHD is no longer being made, but it is almost identical to a xrgb-3 in clarity on a CRT and just as good on a LCD.. the x1920 I find to a bit more blurry than either one, but probbaly still the best up-scaler out there next to the xrgb-2/3. It does have some very very nice cord management features though.
My main test was on Metal Gear Solid 3, Shadows of the Colossus, Ninja Gadien Black and some neo games on my xbox.
Basically the colors on the x1920 are much more hazey than the XRGB-3. The WSHD has darkening and lightening issues. The XRGB-3 gets some noise when doing d-terminal with a PS2/GC/XBOX and the kworld gets none at all. Really unless you are looking at the XRGB-3 side by side with the KWorld systems, you are not going to be hit with a major difference.
edit -
I found the TV Box WS Pro HD for sale here.
http://www.digiparks.lv/public/?id=218&ln=lv&bt_id=11184
Be warned it isn't the best thing in the world for trinitron CRT monitors. I had to amp down the signal do to the fact trinitrons amp the signal so high. Also on 640x480 the image is interlaced.