Enjoy your faulty games, pitiful compatibility, and having to use paper to make the unit fit inside your NDS.
You should realize that all those established and beloved GBA flashcard makers (M3, supercard, etc) are just squeezing every penny they can for a GBA product and spin it as a DS product?
Have you ever stopped to think about the fact that you are playing DS games from a GBA slot?
All those GBA flashcards need to have the DS games patched in order to make them work; This inherently means LESS compatiblity than DSX.
DSX is a native DS slot device with
reprogrammable hardware.
It is obvious that the current hardware solution they have is not working so good. But know what? That is no problem!
Here is the fun fact.. they can change it with a simple firmware upgrade to make some
completely new hardware layout (for those interested, read up on FPGA on wikipedia) to run DS games natively.
What do you have then? A hardware solution with 100% compatibility that runs DS games
NATIVELY.
I put emphasis on NATIVELY alot here in this context because it is very very important to grasp in my hypothetical situation.
Now.. on to a very hypothetical situation which will break your favourite GBA cartridge with DS support:
Suppose Nintendo decides to take measure against piracy on DS. They add in their SDK a magic function called "SDK_CheckHardware()";
What this SDK_CheckHardware does is very simple; It calculates a hash checksum from the DS ARM9 and ARM7 executable binaries and compares this with a hash checksum in the DS header somewhere. It sees that the ARM9 binary has been patched (thank you M3 and Supercard), and refuses to load the game; or worse, Nintendo decides to brick your DS.
Now the only flashcard which will run this game is DSX because it does not need to patch it (more on this later, see 1).
Now some might say "oh but then M3 and Supercard will just release firmware updates to fix this SDK piracy protection".. But keep in mind that Nintendo is not stupid and knows this can happen too.
What to do? Simple again. The SDK function SDK_CheckHardware() can be encrypted with a key specific for a game (randomly generated; this is possible and very easy for Nintendo since each game already has a seperate syscall.a library).
That leads to a situation where M3 and Supercard will have to patch *each and every game* individually that uses this SDK in the future.
Simply put.. not fun at all.
Note 1) I don't know if DSX patches or not; But they have reprogrammable hardware, and this means they can reprogram the hardware to make it NOT patch when they find a proper solution to do this.
These are just my 2 cents.
Oh and don't get me started about the poor support and crappy looking OS loaders for M3 or Supercard..
In summary:
Even though the DSX seems to have only 98% compatibility, reprogrammable hardware will make sure DSX will stay at the top.