I use 2 controllers often, so I bought 2. For regular saves, I bought one of the 4 page jobbies that quadruple the storage of these in the same amount of space. I just slap that one in the first controller's second port. There's no display on the larger memoried one. But that does mean I forsake the use of the vibrating gizmos. But since I've never tried one on the DC, I don't feel like I'm missing anything.
The price is steep, but I prefer getting it from Sega than someone else. Had they produced one of the modules that stores more like the others, I'd have gotten that from Sega as well.