plastic impression stamps. But I've never made one out of ninjaflex until now. Does it work? Actually, yeah, more than I expected anyways. The top finish isn't quite as smooth as a traditional stamp, it works best if you put something soft under the paper to add some flex and increase coverage, the lettering turned out more readable than I though it would.
It still has the same limitation as the impression stamps: line thickness and whatnot. So details have to be chunky. I heard someone mention making the stamp in negative and using a liquid rubber as a mold. So put that on my future project list.