I just received a Beattie Intenscreen last Thurs for my 4x5 field camera. It's a great deal brighter than the glass that came with the Shen-Hao and I already found it helps a lot for composition and focusing.
You do have to move your eye in line with the screen to focus specific areas. But this was necessary in dim light situations with the orig screen anyway.
It is a little difficult using a loupe because of the pattern on the fresnel lens, but I've had success with a 4x loupe (wouldn't try anything with greater magnification). For the basic initial focussing it's excellent. Have even set the plane of focus without a loupe - something I could never do with the old glass screen.
All in all I would agree with Jorge, it's has been a good investment for dim light situations.
L Gebhardt - don't know what the Shen-Hao comes with, but I recon I could make one as good with an old window pane and some sandpaper