Yes I got the MBL DLC. In my opinion, it should have already been included on the game, since there was an option for it from the get-go. However, it does include quite a few balance tweaks, new difficulty level, a new character, and a new stage. Once I got MBL, I had a hard time going back to the old version. It "feels" more complete, and I like the fact that powering up is easier and happens more frequently...then again maybe that's just because I suck at shmups...
If you have any questions about it, don't hesitate to ask.
Note for achievement whores: your normal DS achievements DO NOT unlock if you're playing MBL. Even the ones that require you to simply clear the game.
Note about downloading the DLC:
You need a Japanese XBL account (easily obtainable). Once you download the content, you need to make sure that profile is signed in when you play DS, otherwise the content will not be found. You can have multiple profiles signed in on a 360 at once, so yes, you can unlock MBL achievements on your US/EU 360 account. Make sure your gamesave and the DLC are on the same storage device as well. If you have trouble getting the DLC to show up, send me a PM.