Calling on old electronics training, I suspected a double or even a triple fault. So, using the spare router, I put a tiny piece of steel wire in the 5db aerial connector so that it reached the router pin. It worked! but still not quite as good as they tiny kit one.
Okay, so now why the big one not working? It's sealed into a rigid 'glass' tube, but when I invert it, it clonks from within. So, maybe fault 2.
Wire to this one is okay measured with a test meter. Pins well engineered - but I did the trick of extending the connection. Poor signal, but now it was at least there.
Tried different channels on the basis hi-gain aerials might be finely tuned to one frequency. Slight changes, but nothing that would account for such a low signal. Put diddy one back, and 5 bars again. Still flummoxed - as are the computer company owner than loaned the kit and my ex IBM pal oooop north. "It/they should just work."