1) Single detent (under the top tube).
2) Different pump handle with dual pump arms.
3) Back Block different to accept dual pump arms.
4) Top tube is removable to accept different top tubes (Left, right, and center feed). This is held on with two t-10 Torx Screws.
5) Vertical ASA is not integral (it uses a bolt to hold it on).
6) The top tube can be ordered to accept sizers that allow for one barrel to be used with many different sizers.
Bottom tube internals are the same and, in my opinion, they perform nearly exactly the same - in that they are awesome!