I found two main differences between the interviews at RB and AT Kearney/BCG:
1.: RB makes you do a computer-based test (numerical, verbal, figurative), so a classic IQ/GMAT test. You need to reach a certain score there to pass to the next round. Although BCG also has their 'online case', it is less of a classic test format and more problem solving/maths/understanding the case. Also the online case at BCG apparently is less important than the interviews, whilst at RB it is weighed equally.
2: The interviews at RB are split between personal fit and case. So you have one 1-hour interview just on your CV, personal fit, etc., and one 1-hour interview just on a case (of course with a really brief personal part in the beginning, kind of 'get to know you'). I found the case to be quite different from the regular cases, more focused on techncial knowledge and details and less on strategy. I didn't have to do any maths (one multiplication), but have heard from others the same day that they had a lot of calculations.
What this means for your preparation: if you are not confident in tests and the pressure they entail, it might be good to practice. For the case, try and really get your technical skills (in your field) straight, maybe read some old textbooks etc..