I think for lighting your average rail, work lights do just fine.  You can thrown them around, and if one breaks, you just buy another.  They're almost disposable.  A broken work light every month or so is no big deal, but a broken DP light is a big chunk out of the wallet.
The DP's are nice, but all you're really gaining is more control over your light.  If you really need to control light spill, just buy a roll of black wrap, it will do the trick.
http://www.filmtools.com/roscin24x25.html