Yes it's worth it as there are weekly CC freerolls
and money added buy-ins on both sites.
You mentioned rakeback - I'd go to any rakeback site (check by google) and see what they offer.
Download the carbon and ub software with the provided links.
Don't forget to add your site-nicks in your user cp here at CC.
I find both carbon and ub being a bit softer (looking at micros) than the major sites.
Tourneys and stts don't fill up as fast as there, though.
Less volume in players most naturaly.