These strings have been reported as a favorite by everyone from orchestral bassists to rockabilly players; their soft feel and darker, gut-like vibe (but durable steel construction) can actually make them a good choice for slappers who aren't getting what they're looking for from gut or synthetic strings.
Rockabilly players often choose the Dolce (light) model for their lighter tension, which makes them more slap-friendly.
String gauges (mediums):
G: .051/1.31mm
D: .064/1.64mm
A: .079/2.02mm
E: .109/2.79mm