I picked up a decent Walther CP99 air gun 5 or 6 years ago and have been shooting it a *lot* in the past year.
This particular gun weighs in at 26 oz loaded and is a very true reproduction of the Walther P99 9mm. It's a DAO gun and has a very smooth trigger. You can manually c0ck it for SA but I shoot it DA most of the time. It has 8 round magazines and shoots .177 pellets. They go for around $150 new.
I've been using it to practice draws, quick front sight acquisition, and rapid fire--stuff you might find useful in SD situations. I have a trap setup in the garage so I can shoot from about 20 feet. The shooting range where I typically shoot allows double-taps but no rapid fire, so it's nice to be able to practice rapid fire with a DA trigger.
I didn't realize until a couple of days ago but the grip angle is pretty close to the CW9 and it also has a very similar length trigger pull. The CW9 weighs 22 oz loaded so it's 4 oz lighter. The grip on the CW9 is a bit narrower as well.
The biggest downside is the lack of recoil. As you can imagine at 26 oz and shooting 8 grain pellets at 350 fps, there isn't much kick
All in all I think it's a great tool for practice and It's nice to be able to shoot 250 rounds for about $4 counting pellets and CO2.