How Reliable is it? SD slot can be a bit iffy if your are ejecting the SD and reinserting it a lot. I only noticed this while populating an SD and testing every US/English ROM for MAME. Lot's of downloading, writing to the SD, deleting, etc. Beyond that it's been completely reliable so far.
How is the OS on it? I'm not a fan. Let's be honest, the bulk of what you are going to be doing w/ a DS flash cart is playing DS games. I want my flash cart to go straight to the menu from which I select DS games; homebrew or other wise. I do not want a menu in front of it that allows me to select things, like media playback and other shit that I rarely do on my DS. I'd really rather the plug in menu be something I access from the DS game selection menu, not the other way around. Making things you play frequently a "plug in" isn't really a good option, IMO, as the plug in menu isn't designed well for that... Even w/ the switch I made to iMenu, I still don't see that as a good option.
This, IMO, is actually the biggest failing of the DS2 and why my EZ5i still spends more time in my DSi than my SCDS2. The R4 put that stupid menu in the way and almost every flash cart manufacturer has adopted it. It's patently dumb for any flash cart that is designed to play "backups".
Dear Super Card team: I would like small icon mode, and I would like the SCDS2 to remember the last game I played and start EOS w/ that game selected. Make the shoulder buttons page down/up the list of games. I do not need a second back button, the B button is just fine. See above for what I think of the plug in menu. And I loath the way the save files and such are left out in the root of the SD.
How well does it emulate GBA? Works about the same as GBA on a PSP. Some things work great "out of the box", other things need messing w/. Some things will never work no matter what you do. I have a DS lite (and a slot 2 device) and a PSP. I do not use my SCDS2 or PSP for GBA. It's usable on the SCDS2, but it is not the "real thing". I also do not use my SCDS2 for SNES, my PSP is better at it.
What about DS Backups (Any issues at all?) Damn near flawless. I haven't found anything that doesn't work on it... But then I don't test every scene release either.
I use my SCD2 over my EZ5i in three situations:
1) Software that uses the SCDS2's CPU
2) I want to use free cheat
3) Something doesn't work on my EZ5i
1) Duh.
2) Who else offers this?
3) Kinda answers the question about playing your pirated DS games, huh?
It's a great cart. It really is... But it didn't stop me from leaving my DS lite in my back pack for GBA (my DSi is almost always in one of my pockets unless in use, but my DSlite and PSP live in my bag). It didn't replace my PSP for portable emulation of other devices (SNES,etc). The few things that are broken on the EZ5i that work on the SCDS2 are pretty much all things I don't give a crap about. And I hate the SCDS2 interface, but I suspect if you are upgrading from any other R4-style-start-menu-having cart, you won't notice how annoying it is.
Edit: Want to add DSX86 is awesome. I'm insanely excited about the SCD2 version and what it might shape up to be. There isn't a better replacement on any handheld I own. If it evolves to do 386 emulation as well as DSX86 does 286 emulation than that alone will probably make the SCDS2 my "most used" cart.