Take with a grain of salt, because I am certainly no Markman... but general consensus among the community is that the Brawl Stick is basically a 360 mod of the Wii TvC stick, not the SSF4 SE stick.
"What's the difference?" You ask? It's, in fact, significantly better than the SSFIV stick in almost every way! To be more specific, it basically appears to be Madcatz attempt to perfectly (as perfect as legal anyways) reproduce Sanwa parts using their own fabrication company instead of paying Sanwa's bills on top of that. The short of it is if you look at a Brawlstick button and a Sanwa button they look mostly identical except they seem to wear a lot quicker and I ended up replacing mine in the first week and never looking back...
If you look at the brawlstick "stick" though it's a near flawless copy. The only change (that I could tell anyways) was in the stiffness and length of the spring. Here's the thing though, this is gonna be all personal preference... but in my personal opinion the Madcatz spring is actually significantly better than the Sanwa one! It's stiffer, it's longer, and it just gives the stick this "snap" that I really like. That said, I'm a bass player and you could stiffen that spring up another 2-3x and I'd probably like it even more so again--personal preference.
Anyways... TL;DR you can almost certainly save ya some coin (and a decent dinner out) by just buying a spring for that stick instead of a whole new stick from Sanwa. You shouldn't be able to tell any difference whatsoever.
Just my $0.02,
tehm