I had a Rossi in .45 for several years. Was packed completely full of what looked like wheel bearing grease when I bought it. Took a lot of time with a nylon brush and break parts cleaner to get all that crap out. Bought a spring kit from Brownells shortly afterwards and gave cowboy action a try. Turns out it really wasn't for me.
Overall the gun was pretty decent. The buckhorn rear sight was pretty awful, and tended to drift on its own. I drilled and tapped it for a brass set screw. I installed a set of tang sights, but I did a pretty poor job of it. Cycling was pretty rough originally, but a few hundred rounds down the tube slicked her up nice. The bore was fairly rough, and tended to lead a bit (never fired a jacketed round down the tube). The rifling was also fairly shallow on my example (much like you would expect for a .45ACP), and the rifling was deeper near the muzzle. 50 or so paper patched 240 grain FP boolits smoothed up some of the rough machining in the bore, but it wasn't perfect. Never got 185gr SWC's to cycle correctly either...which is a shame because they would have been a blast.
The stock was not very well inletted. The plastic butt plate cracked when my wife bumped the concrete bench while reloading. The finish they used also was short lived on the pistol grip and forend...might be a good idea to apply something to the stock if you ever plan on wearing gloves while shooting. I ended up using some Birchwood Casey where the leather from our gloves wore through...it looked terrible.
I ended up trading it off, mainly because I was concerned a heavy .45 load for the Ruger or Marlin would accidentally find their way into the Rossi (I've been told they won't handle many of these upper level rounds, and I didn't want an accident to occur). Seems odd since Rossi makes a .454 on the same frame, but I wasn't in love with it enough to experiment or take the risk. I think I ended up trading it straight across for a fairly beat up Marlin in 35 Remington. Both parties felt they got a good deal I believe.
I'd buy another one if I was looking for a fun gun for kids. The current examples I've seen at the range look much nicer then mine did. The sights are much different, and they no longer seem to have a plastic butt plate. Looking on their website, it appears all of them now ship with a more correct looking "92" style stock as well. This time around I would just want to inspect the rifle well to make sure I got properly fitted wood.