Another thing to have on account is how the epub is coded. Some designers force a particular font. This disables the option to change font-face. I've seen it in some epubs and mobi/KF8 without DRM.
Some even have the font forced to serif or non-serif (which I particularly hate
)
The advantage of not having to deal with DRM is that (if you know how to handle CSS) you can customize the ebook as you like...
I'm very gratefull to those publishers that don't make use of DRM