In case you're confused by chartbundle's reply, flight plan cards are their own separate entity, I believe to migrate a flight plan from one 430w to another. That's it. And I can't see them being useful at all.
On top of that, there are navdata cards and terrain cards. And those are not interchangeable, either. Easy way to think about it is that there are three types of cards and none of them are interchangeable with each other.
Having said that, Navdata and Terrain can both be updated from the same usb reader (garmin's usb adapter for garmin updates or jepp's usb adapter for jepp's updates). The cards will work in either reader, but the software is tied to the reader (ie flygarmin uses garmin's usb reader and jepp's software uses jepp's reader.
I recently bought and installed a 430w. It's a jepp-decal'd card that had jepp nav data on it. Bought the garmin usb adapter, installed garmin software on my computer, paid for the garmin subscription instead and uploaded garmin data onto it. Works fine. Garmin readers are the same price as jepp readers, but the subscriptions are cheaper, cheap enough to warrant a switch.