Roger,
I have the Xtreme Extension from Price Cutter which is of similiar design, except the chuck is bigger and there is an allen set screw to tighten the bits in the chuck. I have used it on several projects and I like being able to change bits above the table. I have both the 1/2' and 1/4' collets. I have had no problem with slipage or such, so I don't worry much about a bit coming loose and flying across the shop (which is scarry).
Jim in Mayberry