Welcome to Librarium Online!
They are a poor choice when compared to other units in the book. With the new swarm rules and their low toughness rat swarms accomplish nothing. Rat ogres have no armor and don't hit hard enough for their points. Skaven win with their shooting, magic, and big blocks of CR. Units like slaves and giant rats are better non clanrat choices as they can bait and redirect charges which exposes your enemies' flanks to big CR block charges and deadly ranged fire.
It is way too easy to panic rat ogres. Not to mention what are you really getting?
3 weapon skill 3 str5 attacks per model. Only tough 4, no save. 50 points each. Leadership 5. Every regular ogre unit is better. and many cost less.
I would only take them with a grey seer, and I would frenzy them ASAP.
IMO they are the closest thing the Skaven has to something in the role of cavalry. Bearing in mind they charge 12 and have some punch, I don't think they are that bad. The main problem, as mentioned before, is the cost and low leadership.
"Listen up you primitive screwheads, this is my BOOM-STICK" ... Ash - Evil Dead