Slappers provide a sensation similar to those of paddles, but with a little extra "slap" from the second layer of leather. Experienced dominants can provide more sensations by using two slappers at the same time, playing the submissive like a drum.
Depending on the strength of the stroke, a slapper can provide a light sensation that doesn't mark the skin or a hard slap that leaves welts behind. As long as the partner's limits are respected, a slapper can work for both beginning and experienced BDSM partners.