I have 3 lights kind of like this back from my pizza delivery days (great for shining on houses to see the address) and:

1) Way too freaking heavy and bulky. Depending on the size of the 6 volt SLA battery, it could weigh 5-10 pounds total and most of those are about 6" across on the light lens.

2) As was mentioned before, too narrow a beam. Great for SEEING down the road with, but wouldn't make you seen all that easily. There's light scatter that is really wide, but it's also very, very weak compared to the focused beam.