One of my collegues at OW Dubai was ex-RB so happy to provide some perspective.
Overall they are a well regarded shop in Dubai. Unlike MBB and OW in the Middle East, they do quite a bit of non-public sector work. Clients mostly include big manufacturing companies and oil & gas. RB could be a good place if you want to get staffed across the Middle East [MBBs you will find tend to me more KSA centric].
I haven't heard many positives on the office culture. Being a smaller shop, projects tend to have very lean staffings, resulting in longer hours and high pressure. Given the non-public sector work, the project budgets also tend to be squeezed and as such perks are definately not as nice as the other top-tier consultancies.
Hope that helps.