We used to use Epsons and manually flip, but just within the past year we got an ImpoProof with Canons.
Epson backups weren't great, but were (for lack of a better term) cheap, made ok use of paper, and gave us some flexibility to print on other media for special projects if needed. The downside, was that it took time out of an prepress operators day to flip the sheet. The ImpoProof backups are almost spot on, not cheap, make better use of paper (unless you need a "hot" proof), but the downside is you can't print on any other media. The upside, the prepress operator really doesn't need to do anything except empty the "basket" on occasion. It's pretty much, send it and forget it, unless it is "hot". Or you need to change the roll of paper.
Like MacTwidget says, the software is a bit quirky, but with a bit of time, you will understand it. If it's working right, you really shouldn't have to touch it, until you need to load paper. Or like us, the power goes out, and the computer shutdown.
Tech support for ImpoProof has been very helpful and responsive.
Overall, we've been very happy that we have switched from Epsons to the ImpoProof, wish we would have done it a long time ago. For our shop, I believe the time savings of the prepress operators not turning paper and the savings in paper should make this a good ROI.
