I personally wouldn't buy one.
I haven't had any friends that shot any better with a rifled choke than a good rifled slug. Also, I have heard one account of a 3" slug tearing a rifled choke out of a gun. Don't know if it is true, but that was the story ... and we weren't drinking yet.
Biggest thing to think of is what you asked already - Is two inches enough length to spin and stabilize a slug?