I don't think their comment is intended to be negative really -- looks more like appreciative of the option, while cognizant of the fact that using it introduces a new challenge.
> This is because Zing uses a unique collector called C4 (Continuously Concurrent Compacting Collector) that allows pauseless garbage collection regardless of the Java heap size.
This is incorrect. Firstly, C4 triggers two types of safepoints: thread-local, and jvm-wide. The latter can easily go into the region of ~200 micros for heaps of ~32GB even when running on fast, overclocked servers.
Secondly, the design of C4 incurs performance penalty for accessing objects due to memory barriers. This impacts median latency noticeably.
You might not believe me, but ask Gil and he'll openly admit it. This article was written by someone who:
1) doesn't know how C4 works
2) doesn't analyze relevant metrics from their JVMs