Need Info On Broadcast Spreader That Works Near Edge

There is a relatively new broadcast spreader called "Edgeguard". It is supposed to allow us to use it near the edge of a lawn without worrying about spreading herbicide into the flower bed. This new broatcast spreader has a shield or something that prevents herbicide/fertilizer from spreading into the direction of the shielded area.
My questions are:
- Does the shield really work?
- Does the shield cause a lot of herbicide dumped right under the broadcast spreader?
- Any other downside (other than the high price)?
Thanks for any info.
Jay Chan
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