I've a King Ratty and for what it is, it's a cracking little gun.
I use it for short range around barns and buildings. Very quiet (with a mod on), accurate and powerful enough for what I need it for.
If you're thinking of one as your main gun, however, I'd look elsewhere. Power drops off when it gets below 5 deg C, you need to keep careful count of your shots as the gas runs out with little warning, the build quality's not too good, if you shoot a lot, the 88g canister's soon ramp up the cost and to cap it all it's bloody American!
Maybe have a look for a used Lightning, Webley Xoc