Took my SP101 with CTC to the range yesterday.
At ten yards, in sunlight, the red dot was barely visible against the orange circle at center, and virtually invisible against the white paper.
OTOH, it works very well at indoor ranges, and in the dark.
When it is visible, it is helpful, both for training, and for hitting a target. However, it may not always be visible. (Also, you have to remember to switch it on at bottom of grip, and then grip it properly with middle finger. With the length of my fingers, this is a bit of a chore, since my middle finger is long enough that it floats a little in front of most front straps. For me to use the CTC, it actually takes a bit of mental effort, and a finger move similar to playing guitar...)
But I do think they are worth the money, so long as you train around their limitations. You really do need to know how to use the sights, too, though.