I tried various fancy holders, but in the end decided that I'll likely have to make my own holder from aluminum or steel sheet metal. And even then you run into the problem of lengthwise curvature. For those that are unaware of the problem with this, these scanners have a very limited depth of field, in the range of 1mm or less. So if your film is bent, some of it will always be out of focus.
I can't see much on this fancy webpage, because they made it so fancy that some of the images do not load and those that do load are oh so mysteriously dark. But if their scanner can scan both heavily curved rolls and strips, I will be buying it.
As to optical quality, if you can get your film to stay flat, this is a solved problem, that Epson mentioned above can produce fantastic results (more pixels that you want, generally).