I wonder why both the ESM1 and TesterLinc were discontinued at almost the same time... Could it be that people have been using these tools to get their X10 systems working well, and don't have to buy new equipment? Nah, the manufacturers wouldn't do something like that, would they?
As far as I know, the only testers left are the real basic one produced by X10 (also sold by Leviton), and the Monterey Power Line Signal Analyzer. That is a very nice unit, but it is pretty expensive for most of us.
If there is enough interest, I might consider offering a basic meter that displays background noise level, signal strength, and good/bad commands. With a simple LED bargraph display, a kit could be under $50. For a few dollars more, a transmitter could be included to report line status in response to a query from an automation controller.
Jeff