Yes, I had issues with the MMP internal BEC and the cap fixed the problems for me. It helps reduce the "brown outs" caused by the voltage dropping in the internal BEC. Some servos cause the issues more than others, if they are very high-torque and power hungry.
You want a cap described as "Low ESR", rated for about 10-15V, 105C, and approx. 1000-3000 uF
Any link of where to buy it or see it directly please?? I'll have to try to find it here in Italy and right now I don't find the right "translation" to describe it here...just let me see it trough a e-commerce shop please..