As with any chemical, when used properly, bleach is entirely safe. I have used this technique for 3 or 4 years now and have never had any problems. No damage to shrubs, plants, grass, concrete or people. No matter what you use, if you read the label, it will tell you that it is harmful if used improperly.
As to the evenness - I usually apply the bleach after washing the concrete. Since the concrete is clean, there is no problem with blending, as you will just be removing spots from clean concrete. I suppose that if you found an unevenness in the color, it would mean that the rest of the concrete needed it too - but I have never found this to be the case.
If you have a reasonably clean drive with leaf stains, it can be cleaned with just the application of bleach. I have several customers that like to keep they're drives clean. I wash them once a year and rinse them as needed to control the stains.
Aside from the effectiveness of this method, the cost is another major factor. One gallon of bleach ($2), or a half gallon of chlorine ($1), is enough for most driveways.
Another use for downstreaming bleach: If you are using oxalic acid (or any acid for that matter) on a drive/walk and find it is browning out the grass - simply downstream some bleach and it will neutralize the acid and restore the grass (if done in a reasonably short amount of time.)
Having written all of the above, it just occurred to me that I had neglected to mention rinsing. I always rinse after applying bleach to anything.
