Can anyone offer an opinion on handlersocket vs memcached performance in MySQL 5.6
I would recommend using InnoDB memcached over Handlersocket.  The advantage of InnoDB memcached is that:


It uses a standard memcached protocol, with drivers available for many programming languages.
It does not automatically allow access to all tables in your database, but instead tables 'opt-in' via a mapping containers table.
It has a stated support policy of 8 years.  MySQL 5.6/5.7 support already exists for InnoDB memcached, and these version upgrades are required to unlock many of the scalability enhancements.