Some clarifications:

1. The implementation is experimental in the sense that it was newly introduced it in this release. But I guess it is actually quite stable (it is based on klibc). Only the floating point stuff is new (and probably not fully IEEE 754 compatible), but strongSwan uses this only very rarely (actually on Mac OS X this functionality is not used at all).
2. It also implements all the features needed by our own code, but it is less complete than the other two implementations mentioned in the changelog.
3. The performance is not really an issue in client scenarios, which is the use case here.