Inserter code (not counting the fluid inserter) has to be overhauled (after the release), because of its poor performance and badly organized code.
@Pabilo8 :

• Create InserterBase class, for basic methods for item inserters
• Make the inserter use lambda predicates and functions instead of the "wall of ifs"
• Separate list / map for input and output functions
• API for the inserters for easier integration
• Handler for default methods
• Implement such expressions and functions
  • Implement #18 (kinda common topic)
• Common data handling code