There are two kinds of stamps: Preinked and Self-inking. PJ Invites Stamps are preinked and there is significant difference from the self-inking stamps.
Self-inking stamps rest on an inked pad and then rotate to hit the paper. Preinked stamps uniquely have the graphic/text on the rubber die which itself is impregnated with ink. The background of the special die is sealed so no ink gets through except where the graphic/text is.
No extra movement, therefore, no blurring. No excess exposure to ink, therefore no messy blotches.
Self-inking stamps uses a water-based ink. Preinked stamp use an oil-based ink.