Many sellers offer these upgrades without fully explaining what they are.

The Pismo predates CD-RW, Combo and Superdrive technology. 

There are some, very rare, purpose made third party CD-RW drives which replace your entire DVD drive and have a Pismo styled casing. 

However, most "upgrades" consist of a replacement mechanism, and use your existing DVD module, replacing the Apple DVD mechanism with a different one.

The upgrade is easy to install, just a few screws, but be aware (and many sellers don't warn you), that the drive may well come without any sort of bezel (front plate), or a PC style one, and your existing bezel won't fit on it.  It *might* be possible to make it do so with work, but generally not.  This will leave your Pismo's smooth lines looking a little strange with either a PC style bezel recessed or protruding, or no bezel at all - leaving your Pismo and your drive open to dust etc.

That having been said, mechanism upgrades are a great way of giving enhanced life to an aging Pismo or to replace a failed DVD drive.  In fact the way prices have gone, it costs little more to replace a failed DVD mechanism with a Superdrive than it does to replace it with a DVD.

We supply a number of different drive upgrades, these have all been tested in a Pismo, are bootable and supported by Disc Burning in OS X 10.4.  They usually work with earlier versions or with PatchBurn software. 

Where possible these will be supplied with the original bezel for you to decide what you would like to do.