A few things to keep in mind with the Paterson:
They come with an attached loading lever or a separate loading tool. If you buy one without the loading lever attached, make sure it has the separate loading tool with it - they are expensive to buy and sometimes hard to find.
Patersons are known to jam from cylinder pin fouling. On mine, I use lube pills (beeswaz, paraffin) or, even better, the vegetable spray PAM. Works great.
If you do get one, and you do shoot it, you will want to clean it. I strongly suggest taking pics of each step of the disassembly process - they can be tough to put back together the first time.
They are great shooters, lots of fun, but in a class of their own.