That seems like a good idea BUT allot of trouble to make. I have two much easier things that I use to do the same thing.
The first is to use a telescoping magnet to reach under the bench. It looks like a pocket pen but telescopes to about 24" long. Used for metallic items.
The second is to use for non metallic items. I place a small piece of nylon hose ( old panty hose) over the end of my shop vac using a rubber band to hold it in place and it sucks up the dust but, larger items are stopped by the hose and when the vac is shut off the item drops onto the bench.
Just my two centavo's worth.
Rog