This is just my limited view of what actually happened, if I'm wrong, or missing something, someone please correct me.
MSET is just an entrypoint in a chain of exploits that was used back on firmwares 4.0-4.5 or somewhere around there. The Later firmwares patched out other stages of the exploit chain, and eventually the entrypoint itself was patched out.
When gateway released their browser(spider) based launcher, in, what I'm assuming was an effort to keep things simple, they re-did their launcher.dat to work through old mset AND spider. Of course, this left n3ds users boned because the the n3ds was incomaptible with both(too new for old-mset, and different browser (skater)), so eventually, they exploited Ocarina of Time and Cubic Ninja so that n3ds users could launch gateway.
Once gateway team found out how to downgrade system titles, gateway updated the mset portion of their launcher.dat to use newer exploits, since cartridge swapping makes flashcard use a pain, and the two main exploitable games (Cubic Ninja and Ocarina Of Time) have skyrocketed in price. Either that, or they just felt like being nice for some reason.
The problem is, spider and cubic ninja's stuff has pretty much been laid out for everyone to easily use, while nobody apparently has or cares about OoT, and even fewer people care about new-mset.
Sadly, the end result is that, a launcher.dat style program isn't usable with every exploit, only the ones it was designed to work with. Unless the developer of said program explicitly states that it's compatible with new-mset, it's more than likely not going to work.
EDIT: Added standard disclaimer to the top, I can't/don't-care-to be everywhere and know everything about the scene and what's happened.
