I've never used dyna beads but I used to use balancing dust in my truck tyres. The only problem I came across with the balancing dust was that you had to use an air drier on the airline system to stop the dust clumping. I'm guessing that you wouldn't get that problem with the beads.
Did it at the end of work today, and the drive home was definitely smoother, so I guess they work... but will have to see how the work over time.
If you do go down this route, they can be installed on the vehicle... get their installer, and I used an old set of hair clippers with the blade removed to provide vibrations that help the beads flow faster... took about 5 mins per wheel.
I believe there's a conversation on noisy's build thread, or there's a thread somewhere with a discussion involving noisy about these as when I read it I thought about using them myself...