Those single-shot break action shotguns can be a little bit rough to shoot. This is because they're somewhat light-weight, which makes recoil a bit more stout. The price is good on them, but the recoil issue can actually make them a somewhat poor choice for new shooters.

Personally, I would look around for a Mossberg 500 Bantam 20ga. The going price on them seems to be around $280. Great all around shotgun, as you can adjust the length of pull to match shooters of all statures, it has a comparatively short 22" barrel (makes it easier to maneuver), and it accepts choke tubes. Plus, unlike the Rossi, it's pump action with the ability to hold 5 shots.

A lot of people say to go with a 12ga, and there is a lot of logic in that, as 12ga is the most common shotgun chambering by far and, because of this, it's very versatile. However, I'm also a big fan of 20ga shotguns. You don't really save any money over a 12ga, but what you do get is a gun that's typically a little lighter, swings faster, and is handier, without as rough of recoil. Also interesting is that, while 12ga is most common, sometimes it's easier to find 20ga shells than 12ga, as they're still extremely common but with slightly less demand.

Finally, one really nice thing about 20ga shotguns is that the standard buck load for a 20ga is ~20 pellets of #3 buckshot. This is just about a perfect home defense load.

Massad Ayoob (a well known firearms instructor) had a neat article on the 20ga shotgun a while back. Basically he said, unless you are going after big water-fowl (or big-bear), a 20ga shotgun can do everything a 12ga can and is arguably better at it. It's a good read:

http://www.backwoodshome.com/articles2/ayoob120.html