All the features of the Unlimited plan, plus the facility to customise in-skill greetings as well as early access to future versions.
Lifetime members can access an exclusive feature allowing them configure how they are greeted when launching the skill - have Alexa greet you by name, or any way you want!
The skill costs a small amount to manage and maintain. Opting for the Unlimited plan helps contribute towards these costs as well as help with future development and improvements.
Lifetime means for the users lifetime, or the duration for which the skill is supported and maintained.