The name of this company is actually a contraction of Ernst Rodenhäuser. Ero is something of a successor to the Reform company, having bought up Reform’s production facilities in 1956 (this is an earlier incarnation of Reform, by the way; I expand upon that on Reform’s page). I can find little other information about the company, apart from a google search finding them in various German business directories, indicating that they are still in production, making pens and pencils. Some informants suggest, though, that this particular Ero ceased production in the mid 1980s.
Models I’ve examined: