The Postamper Stamp Affixer was made for the Postamper Company out of Chicago, manufactured by International Postal Machinery Company, and distributed by Polak Van Alemlo, Inc. The Postamper Stamp Affixer looked very similar to the Multipost Stamp Affixer, but it had a thicker rounded plunger.
There appears to have been at least two different models of the Postamper made. One had a thinner rounded plunger and one had a thicker round plunger.
Like most stamp affixer companies, Postamper also had testing stamps that users could buy to calibrate the machines. Apparently these stamps are a little more rare than other stamp affixer stamps.