{I am looking at getting a 12 gauge slug gun for deer hunting. I got my eye on a R870. Is it worth it to get a rifled barrel?}
Yes the rifle bbls normally comes with rifle sights. The rifling will let you shoot both foster, brenneke style slugs plus sabot-slugs. Youo will have to try a bunch to see what she like.
I bought a basic 870 and threw on a hasting rifled bbl in both 20" and 24" lengths.
fwiw:the 20" is idea for carrying thru tigher areas.