It would be nice to have a deeper understanding of how/why this works, but in practice it seems fine. Under a continuous insert and erase workload the number of chunks with an overflow fluctuates a bit but stays low enough to keep probe lengths short, so F14 never needs to rehash to clean them up. Batched adds and then removes might let you bias a bit toward having longer probes for the remaining keys, but it never gets too bad. A truly adversarial workload could make things pretty bad, but they could also just insert lots of keys that all have the same hash code.
See the steady_state_stats test at https://github.com/facebook/folly/blob/master/folly/containe...