Effective lime slaking can be accomplished with both Pebbled or Powdered Quicklime.
What’s best for you will depend on your slaking system and your ability to deal with the potential extra dust created by using only powdered quicklime. It is generally not necessary to use this more expensive powdered quicklime to create high quality / highly reactive milk of lime in a lime slaker.
High calcium pebbled quicklime is perfectly suitable for most lime slakers. It is a common misconception that powdered quicklime contains less of a grit component.