So fridges are out, not that he didn't already sort of expect that.
Illusion and information make telegraphs less attractive. Maybe radio. Maybe RADAR, to ease the burden on knowledge mages for air traffic control?
It'll probably have to be computers, though. Annoying. He doesn't know that much about electrolithography and semiconductor patterning, though he's sure he could figure some things out.
...Hmm. He'll have to figure out if knowledge mages can casually stomp all over encrpytion. Selling Nazi-style ENIGMA machines to a weird amoral society would be vaguely ironic. Or something.
More wandering and listening and looking thoughtful.