How much of an upgrade is this from the original? Slightly noticeable? Very noticeable?

Very noticeable if you have a can that has backpressure. Like night and day then.

Do I need a RMA for the swap program?

I thought this was going to be about a tranny that just had a new vagine installed…

In some cultures, a virgin bride is an expectation.  Prior to marriage, some women in those cultures will have a hymenoplasty performed to meet the expectation of their husband.  Similarly, some married women have a hymenoplasty performed, typically prior to a first anniversary, so her and her husband can relive their first honeymoon night.
MHO, YMMV, etc.

That went off course.  

The product was named by guys in their 20's and sophomorically, and I wasn't super big on it, but let people name the product what they wanted to name it.  When we came out with the 2.0 I was thinking we should change the name, and then the 40 year old programmer who is about as conservative as a librarian mentioned he was sort of hoping for, "younger, tighter SNACH" (as in newer and fitting closer which is one of the differences) and laughed.  

And I thought if this family guy could laugh maybe the customers could too. The acronym means Suppressor Normalized Ambidextrous Configurable Handle.   There is a short set of levers available again as it was when the product was initially released, and that set affords the configurability.