Thanks for the details Januz. A comparative review, even if considered biased, it's low degree of such bias will make for a nice ranking and trust if it is from the horse's mouth so to say.
In fact the ease with which FA could be implemented without a ton of ZZ maintenance scripts was what enticed me to offer it to the OpenVZ (ProxMox VE) community and you will therefore see quite a lot of upgrade requests from v2.2.11 (last released OpenVZ template) to the 2.3 versions. From v2.1 to v2.2.11, every significant development state was diff'ed and patches offered to the community, sometimes even twice a day when warranted, that prompted many to take the plunge into FA.