I did a test run on VioVio in January. The quality was horrible. Color casts and shifts on every page, nothing consistent. I did 15 books and even from book to book it was different.
And after I uploaded the file, it was rejected as the page spreads were incorrect, even though it followed their online directions. I emailed them about the discrepancy and never got an answer. The Web site still says to use the spreads but you have to upload single page.
I’ve used LuLu, Blurb, MyPublisher … and VioVio was a by far the worst.
From my experiences, Blurb has had the best quality, both in print quality and book quality. The print profiles they provide were dead-on to the book I got back. And then three months later I ordered another book and it matched the first book perfectly.
LuLu and MyPublisher had the about the same quality, where the printed book didn’t match the original, with some pages having color casts on them.