I can't say how much improvement you'll see with the Canon, but attaching to glass will give you better flatness. I can't fully tell from these scans if that is an issue for you, but you could check for yourself. The Epson on the other hand definitely needs the adjustability offered by the betterscanning holders.
If you are attaching the film directly to the glass, you will need ANR glass to avoid Newton's Rings, or you will need to wet mount, or you will need some ANR spray. For the Canon 9000f I'd just use the ANR glass.
I like the betterscanning system very much, but it isn't that cheap, since it is a low volume product.