There are a couple of caveats there, athlonkmf. The first is that the memory cards will drain your battery faster, though you'll still get 2~3 weeks between charges, so you may not care about that.
The second is that using memory cards the way you describe means that the
Reader has to do all the page parsing, rather than the PC (which is faster at it), and it will re-parse the entire card every time you insert it. That will have an effect on your battery life too, but mostly it's just slow to wait for.
For me, I've found that I prefer to just wait the time that it takes to xfr the files into internal memory. Since I'm rarely moving more than a few files at a time, I don't find the speed to be a burden, I don't have to worry about losing my bookmarks that way, and I get to use collections, which are a particular boon to me.
If you're happy with what you're doing, though, don't let me talk you out of it.