Ended up getting a electronic sniffer leak tester TIF brand XP1A . This seemed to be the best balance of feature / costs. ( ~ $ 150 including shipping. )

It has the vital feature of 7 sensitivity levels and 18 graduations within each level. The audio function is too confusing for the moment. It has a rhythmic beep that is faster at higher sensitivity levels, when freon is sensed the beep turns to a siren sound. It is difficult to make a fine distinction between small changes in the beep / siren.

The visual bar display is much more useful, The 7 LED display starts out green, then orange then red to give the 18 levels. This allowed me so sweep the system at high sensitivity to find the general leak then less sensitive to locate actual leak.

Down sides of this device are: Made in China, plastic box requires the sensing wand to be nearly kinked for it to fit.

I tried the loaner ultrasonic leak tester but it was not too useful even though the leak was large. There was some sense that something is leaking there but I could not home in on it.

Leak turned out to be condenser corrosion directly behind the aux fan motors. This car was a CA car that made it's way to salt areas , back to CA. The car was never driven in enough rain to wash the area behind the fans. Finding this with bubbles would be difficult as the leak turned out to be between fins.