What RetroDefense said is spot on. The disadvantages vary, such as certain Everdrives requiring you to reset the system in order to save games, game incompatibilities, and certain games requiring patches to run. Again, I'm not complaining here, and I highly recommend them, but I want you to know they're not "100% perfect."
It's the launch Japanese Saturns that I mentioned, I don't know about any other models, sorry. Here's some more information:
http://assemblergames.com/l/threads/saturn-20-pin-cd-drive.55417/
http://assemblergames.com/l/threads/official-rhea-discussion.57377/