Dont get it confused with the Express Compact version, which is a smaller & lower power.
There are Tune kits available & it takes a standard 28mm Diana piston seal.
Venoman (Lyn Lewington) did some brass aftermarket replacement triggers which are impressive.
The OEM trigger can be improved by removing a couple of washers from under the forward adjustment screw.
There are some newer vesions that include a thumbhole ambi stock and an underlever variation