Cons, as far as I know, are not much, but yes, no organization is perfect. So, here you go:
1. Streamlining is on the curve these days, many a things alter and you get to know that well in advance, so no worries !
2. Small set-up in India, so you won't have an "office-feel". Its just a suite-office in Vipul Square (Sushant Lok, Gurgaon, Haryana). People hailing from big employers find a reason to call it "withdrawal shock", as they were always surrounded by people with their previous employers . Here at RSM-Gurgaon, you won't see much people in office as there are none. The firm is growing and will eventually add-up to its human capital. Please allow yourselves to relax here.
3. Facilities are reasonably afforded to you. People from large MNCs and firms find it difficult to cope-up with the same. Every organization has budgets, so does RSM. Facilities are reasonably provided - Cafe Coffee Day machine, in-house kitchenware and cutlery, full-time domestic help to run your office and semi-personal errands, cab facilities (male employees - after 9 PM and female employees - after 7/8 PM), parking/ reimbursements in lieu for employees.
4. High-bench time - RSM is just setting-up in India, so please be ready to sit without any project for a while, which should not frustrate you. There is not much work around and verticals are just setting-up.
Other than these, I personally can't think of much negative sides of RSM. Its a small and well-knitted group of people which is growing day-by-day and presents immense opportunities to learn and grow.