I have had the Longbow Previewer for a few years now.
It does give a better preview than without it and gives you useful info about the file by simply previewing it.
However, after using it to preview DGN Microstation files where it lets you zoom and pan around the drawing, I wish that it would do that for DWG files. I do have MicroStation installed so I don't know if previewing DGN files in window explorer doest zoom and pan stuff without Longbow being installed...
The enlarged preview that it produces is static and is dependent on the last saved view when the file was closed. So there isn't much control in that realm. But I really like it and the price is reasonable.