One thing to consider on something like this is that the Tesla wall units apparently have a setting that can turn on/off "sharing" with unauthorized cars (and only Teslas can authorize correctly):
So, even with a fully functioning J adaptor, your success may depend on the proprietor's configuration, whether they set it up that way intentionally or not. That would give me pause on relying on one in a pinch. A working adaptor definitely expands your charging options, but maybe not by as much as it would seem.
At $150, maybe the Lectron is a 'nice to have' tool to expand a few charge options. They used to be something like $400 which is pretty crazy.