I think it will be ok. that add-on thing makes it seem kind of interesting. But the sound aren't going to be that great, and you wont be able to play it on an R4.
You might not be able to buy it separately though unless you bought it second hand. I reckon it's going to be okay, I think there's a way to play it without the addon by using the buttons on your DS.
Convenience purposes? I mean you'll have to carry more than one cartridge around, but maybe that's just me being lazy.
Well chances are they're going to dump the rom regardless. So you'll only need to carry the attachment. Edit: Wrong section