i have 2 48" (2x blue and magenta combo) on my 48" tank coupled w/ a 6 bulb t5ho fixture. It most certainly does NOT add any shimmer to the tank. However, the magenta does add a nice tint to the overall color of the lighting which i like. When the whites come on, it makes it look a little less white.
I personally like them, but the difference is very subtle.