Most e-readers will open PDFs, but they don't present them as nicely as you might like. ReFlower will quickly edit any PDF into a document that looks much nicer on an e-reader. You don't have much control over the product, but you will end up with something that is easier to read.
The download seems to be tailored to Amazon's Kindle brand of e-readers. That makes sense, since they are the most popular and can be temperamental with non-native formats. However, a little more flexibility would be a welcome addition. It would also be nice if ReFlower gave you a preview of the final document instead of just converting it. Instead, you have to pre-edit your PDF so each page ends up where you want it to. This causes more trial and error than is really necessary, but it does allow the program to be fast and light. Though you can't change much about the way your pages appear, you can add columns or change the orientation from portrait to landscape.
If you have already spent a lot of time laying out your writing, ReFlower can make it work on more gadgets with ease. You appreciate the program a little more when you see it for what it is -- a file conversion program -- and not what it could be, which is a dynamic layout program.