I interviewed 6 months ago and got an offer. In the end i decided to go for a big 4. 2 things helped my choice.
The first is that although RB is a tier 2 strat house in the UK ( which is very respectable ) - it is very little known outside of the consultancy industry. You might have difficulties explainng who they are to a VP at BP or Unilever more so than you would, lets say, with Deloitte. If you are in the German office its compeltely different.
Secondly - and this may sound strange - but the feeling I got in thier offices. THey are in Berkely Square (next to ATK). The offices are oldish and tiny - i dont think the practice has more than 25 people working on the front office side.
My advice: you are likely to get better trainin. more scope and breadth of work, and greater marketability at any big 4 / tier 2 consultancies.
This said - you could apply to RB Germany - do two years there, go to McKinsey in Munich and then ask for a transfer to London!
Best of luck