The last group ride I was on a week ago I noticed a regular from our group with a new bike and a flashlight in a TwoFish lockblock. Usually I'd consider those better than the rubber band straps. Nope. Her light popped off on a moderately rough road.
Reminds me, next group ride I plan to ask cyclists using those things to please use backup retention -- a zip tie or something.
I don't disagree with the reasons for preferring a flashlight, despite issues about beam patterns -- that can be fixed with a decent hood, even a homemade hood like I use on my L&M Urban.
My only concern is with the farm rigged methods for mounting flashlights.